Interlayer for laminated glass, and laminated glass

ABSTRACT

There is provided an interlayer film for laminated glass with which the flexural rigidity of laminated glass can be enhanced and the sound insulating properties of laminated glass can be enhanced. The interlayer film for laminated glass according to the present invention includes first, second, and third layers containing a polyvinyl acetal resin and a plasticizer, the content of the hydroxyl group of the polyvinyl acetal resin in the first layer is lower than the content of the hydroxyl group of the polyvinyl acetal resin in each of the second and third layers, when absolute values of a difference between the content of the hydroxyl group of the polyvinyl acetal resin in the second and third layers and the content of the hydroxyl group of the polyvinyl acetal resin in the first layer are defined as XA and XB, respectively, each of the absolute values XA and XB is 9% by mole or more and 11% by mole or less, and when a content of the plasticizer in the interlayer film relative to 100 parts by weight of the polyvinyl acetal resin in the interlayer film is defined as Y, XA, XB, and Y satisfy the equations of Y≤−1.68XA+56 and Y≤−1.68XB+56.

TECHNICAL FIELD

The present invention relates to an interlayer film for laminated glasswhich is used for obtaining laminated glass. Moreover, the presentinvention relates to laminated glass prepared with the interlayer filmfor laminated glass.

BACKGROUND ART

Since laminated glass generates only a small amount of scattering glassfragments even when subjected to external impact and broken, laminatedglass is excellent in safety. As such, the laminated glass is widelyused for automobiles, railway vehicles, aircraft, ships, buildings, andthe like. The laminated glass is produced by sandwiching an interlayerfilm for laminated glass between two glass plates.

Examples of the interlayer film for laminated glass include asingle-layered interlayer film having a one-layer structure and amulti-layered interlayer film having a two or more-layer structure.

As an example of the interlayer film for laminated glass, the followingPatent Document 1 discloses a sound insulating layer including 100 partsby weight of a polyvinyl acetal resin with an acetalization degree of 60to 85% by mole, 0.001 to 1.0 part by weight of at least one kind ofmetal salt among an alkali metal salt and an alkaline earth metal salt,and a plasticizer in an amount more than 30 parts by weight. This soundinsulating layer can be used alone as a single-layered interlayer film.

Furthermore, the following Patent Document 1 also describes amulti-layered interlayer film in which the sound insulating layer andanother layer are layered. Another layer to be layered with the soundinsulating layer includes 100 parts by weight of a polyvinyl acetalresin with an acetalization degree of 60 to 85% by mole, 0.001 to 1.0part by weight of at least one kind of metal salt among an alkali metalsalt and an alkaline earth metal salt, and a plasticizer in an amount of30 parts by weight or less.

The following Patent Document 2 discloses an interlayer film which isconstituted of a polymer layer having a glass transition temperature ofmore than 33° C. In Patent Document 2, a technique of arranging thepolymer layer between glass plates with a thickness of 4.0 mm or less isdescribed.

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: JP 2007-070200 A

Patent Document 2: US 2013/0236711 A1

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

With regard to laminated glass prepared with such conventionalinterlayer films described in Patent Documents 1 and 2, there are caseswhere the laminated glass is low in flexural rigidity. As such, forexample, when laminated glass is used for a side door of an automobile,laminated glass with no fixing frame sometimes causes troubles inopening/closing of the glass due to the deflection attributed to the lowrigidity of the laminated glass.

Moreover, in recent years, for the purpose of attaining reduced weightof laminated glass, use of thin glass has been desired. In laminatedglass prepared with an interlayer film sandwiched between two glassplates, when the thickness of the glass plate is thinned, there is aproblem that maintaining the flexural rigidity sufficiently high isdifficult.

Laminated glass can be reduced in weight as long as the rigidity oflaminated glass, even with the thin glass plates, can be enhanced byvirtue of the interlayer film. When laminated glass is light in weight,the amount of the material used for the laminated glass can be decreasedto reduce the environmental load. Furthermore, when laminated glassbeing light in weight is used for an automobile, the fuel consumptioncan be improved, and as a result, the environmental load can be reduced.

Moreover, with respect to laminated glass prepared with an interlayerfilm, in addition to being high in flexural rigidity, being also high insound insulating properties is desired. In Patent Document 1, althoughlaminated glass being high in sound insulating properties has beendisclosed, making the laminated glass high in flexural rigidity isdifficult. In Patent Document 2, an interlayer film in which a polymerlayer having a glass transition temperature of more than 33° C. and apolymer layer having a glass transition temperature of less than 20° C.are layered has been disclosed. However, in laminated glass preparedwith an interlayer film disclosed in Patent Document 2, the flexuralrigidity of laminated glass immediately after the preparation fails tobecome sufficiently high, and in addition, there is a problem that theflexural rigidity of laminated glass after a certain period of time haselapsed from the preparation is significantly lowered as compared tolaminated glass immediately after the preparation.

An object of the present invention is to provide an interlayer film forlaminated glass with which not only the flexural rigidity of laminatedglass immediately after the preparation but also the flexural rigidityof laminated glass after a certain period of time has elapsed from thepreparation can be enhanced and the sound insulating properties oflaminated glass can be enhanced. Moreover, the present invention is alsoaimed at providing laminated glass prepared with the interlayer film forlaminated glass.

Means for Solving the Problems

According to a broad aspect of the present invention, there is providedan interlayer film for laminated glass, which has a three or more-layerstructure and contains a polyvinyl acetal resin and a plasticizer,including a first layer containing a polyvinyl acetal resin and aplasticizer, a second layer being layered on a first surface of thefirst layer and containing a polyvinyl acetal resin and a plasticizer,and a third layer being layered on a second surface opposite to thefirst surface of the first layer and containing a polyvinyl acetal resinand a plasticizer, the content of the hydroxyl group of the polyvinylacetal resin in the first layer being lower than the content of thehydroxyl group of the polyvinyl acetal resin in the second layer, andwhen an absolute value of a difference between the content of thehydroxyl group of the polyvinyl acetal resin in the second layer and thecontent of the hydroxyl group of the polyvinyl acetal resin in the firstlayer is defined as XA, the absolute value XA being 9% by mole or moreand 11% by mole or less, the content of the hydroxyl group of thepolyvinyl acetal resin in the first layer being lower than the contentof the hydroxyl group of the polyvinyl acetal resin in the third layer,and when an absolute value of a difference between the content of thehydroxyl group of the polyvinyl acetal resin in the third layer and thecontent of the hydroxyl group of the polyvinyl acetal resin in the firstlayer is defined as XB, the absolute value XB being 9% by mole or moreand 11% by mole or less, and when a content of the plasticizer in theinterlayer film for laminated glass relative to 100 parts by weight ofthe polyvinyl acetal resin in the interlayer film for laminated glass isdefined as Y, XA, XB, and Y satisfying the equations of Y≤−1.68XA+56 andY≤−1.68XB+56.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the content of the plasticizer inthe first layer relative to 100 parts by weight of the polyvinyl acetalresin in the first layer is larger than the content of the plasticizerin the second layer relative to 100 parts by weight of the polyvinylacetal resin in the second layer.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the content of the plasticizer inthe first layer relative to 100 parts by weight of the polyvinyl acetalresin in the first layer is larger than the content of the plasticizerin the third layer relative to 100 parts by weight of the polyvinylacetal resin in the third layer.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the content of the hydroxyl group ofthe polyvinyl acetal resin in the second layer is 32% by mole or more.In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the content of the hydroxyl group ofthe polyvinyl acetal resin in the third layer is 32% by mole or more.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the absolute value XA is more than9.3% by mole. In a specific aspect of the interlayer film for laminatedglass according to the present invention, the absolute value XB is morethan 9.3% by mole.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the content of the plasticizer inthe first layer relative to 100 parts by weight of the polyvinyl acetalresin in the first layer is 55 parts by weight or more and 100 parts byweight or less.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, each of the content of theplasticizer in the second layer relative to 100 parts by weight of thepolyvinyl acetal resin in the second layer and the content of theplasticizer in the third layer relative to 100 parts by weight of thepolyvinyl acetal resin in the third layer is 50 parts by weight or less.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the content Y of the plasticizer inthe interlayer film for laminated glass relative to 100 parts by weightof the polyvinyl acetal resin in the interlayer film for laminated glassis 25 parts by weight or more and 40 parts by weight or less.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the polyvinyl acetal resin in thefirst layer is a polyvinyl butyral resin, the polyvinyl acetal resin inthe second layer is a polyvinyl butyral resin, and the polyvinyl acetalresin in the third layer is a polyvinyl butyral resin.

In a specific aspect of the interlayer film for laminated glassaccording to the present invention, the interlayer film is used togetherwith a first glass plate having a thickness of less than 2 mm and isarranged between the first glass plate and a second glass plate toobtain laminated glass.

According to a broad aspect of the present invention, there is providedlaminated glass including a first lamination glass member, a secondlamination glass member, and the above-described interlayer film forlaminated glass, the interlayer film for laminated glass being arrangedbetween the first lamination glass member and the second laminationglass member.

In a specific aspect of the laminated glass according to the presentinvention, the first lamination glass member is a first glass plate andthe thickness of the first glass plate is less than 2 mm.

Effect of the Invention

Since the interlayer film for laminated glass according to the presentinvention is an interlayer film for laminated glass having a three ormore-layer structure and containing a polyvinyl acetal resin and aplasticizer and includes a first layer containing a polyvinyl acetalresin and a plasticizer, a second layer being layered on a first surfaceof the first layer and containing a polyvinyl acetal resin and aplasticizer, and a third layer being layered on a second surfaceopposite to the first surface of the first layer and containing apolyvinyl acetal resin and a plasticizer, the content of the hydroxylgroup of the polyvinyl acetal resin in the first layer is lower than thecontent of the hydroxyl group of the polyvinyl acetal resin in thesecond layer, and when an absolute value of a difference between thecontent of the hydroxyl group of the polyvinyl acetal resin in thesecond layer and the content of the hydroxyl group of the polyvinylacetal resin in the first layer is defined as XA, the absolute value XAis 9% by mole or more and 11% by mole or less, the content of thehydroxyl group of the polyvinyl acetal resin in the first layer is lowerthan the content of the hydroxyl group of the polyvinyl acetal resin inthe third layer, and when an absolute value of a difference between thecontent of the hydroxyl group of the polyvinyl acetal resin in the thirdlayer and the content of the hydroxyl group of the polyvinyl acetalresin in the first layer is defined as XB, the absolute value XB is 9%by mole or more and 11% by mole or less, and when a content of theplasticizer in the interlayer film for laminated glass relative to 100parts by weight of the polyvinyl acetal resin in the interlayer film forlaminated glass is defined as Y, XA, XB, and Y satisfy the equations ofY≤−1.68XA+56 and Y≤−1.68XB+56, not only the flexural rigidity oflaminated glass immediately after the preparation but also the flexuralrigidity of laminated glass after a certain period of time has elapsedfrom the preparation can be enhanced and the sound insulating propertiesof laminated glass can be enhanced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view schematically showing an interlayer film forlaminated glass in accordance with a first embodiment of the presentinvention.

FIG. 2 is a sectional view schematically showing an example of laminatedglass prepared with the interlayer film for laminated glass shown inFIG. 1.

FIG. 3 is a schematic view for illustrating a measurement method for theflexural rigidity.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

The interlayer film for laminated glass (in the present specification,sometimes abbreviated as “the interlayer film”) according to the presentinvention has a three or more-layer structure and contains a polyvinylacetal resin and a plasticizer. The interlayer film according to thepresent invention may have a three-layer structure and may have a fouror more-layer structure. The interlayer film according to the presentinvention is provided with a first layer containing a polyvinyl acetalresin and a plasticizer. For example, it is preferred that theinterlayer film according to the present invention be provided with afirst layer containing a polyvinyl acetal resin and a plasticizer, asecond layer being layered on a first surface of the first layer andcontaining a polyvinyl acetal resin and a plasticizer, and a third layerbeing layered on a second surface opposite to the first surface of thefirst layer and containing a polyvinyl acetal resin and a plasticizer.The second layer may be an outermost layer and an additional layer maybe layered at the opposite side of the face on which the first layer islayered of the second layer. The third layer may be an outermost layerand an additional layer may be layered at the opposite side of the faceon which the first layer is layered of the third layer.

In the interlayer film according to the present invention, the contentof the hydroxyl group of the polyvinyl acetal resin in the first layeris lower than the content of the hydroxyl group of the polyvinyl acetalresin in the second layer, and when an absolute value of a differencebetween the content of the hydroxyl group of the polyvinyl acetal resinin the second layer and the content of the hydroxyl group of thepolyvinyl acetal resin in the first layer is defined as XA, the absolutevalue XA is 9% by mole or more and 11% by mole or less, and the contentof the hydroxyl group of the polyvinyl acetal resin in the first layeris lower than the content of the hydroxyl group of the polyvinyl acetalresin in the third layer, and when an absolute value of a differencebetween the content of the hydroxyl group of the polyvinyl acetal resinin the third layer and the content of the hydroxyl group of thepolyvinyl acetal resin in the first layer is defined as XB, the absolutevalue XB is 9% by mole or more and 11% by mole or less.

In the interlayer film according to the present invention, when acontent of the plasticizer in the interlayer film for laminated glassrelative to 100 parts by weight of the polyvinyl acetal resin in theinterlayer film for laminated glass is defined as Y, XA, XB, and Ysatisfy the equations of Y≤−1.68XA+56 and Y≤−1.68XB+56.

Since the interlayer film according to the present invention is providedwith the above-mentioned configuration, not only the flexural rigidityof laminated glass immediately after being prepared with an interlayerfilm but also the flexural rigidity of laminated glass after a certainperiod of time has elapsed from the preparation can be enhanced and thesound insulating properties of laminated glass can be enhanced.Moreover, there are many cases in which the interlayer film is arrangedbetween a first glass plate and a second glass plate to obtain laminatedglass. Even when the thickness of a first glass plate is thinned, by theuse of the interlayer film according to the present invention, theflexural rigidity of laminated glass can be sufficiently enhanced.Moreover, even when the thicknesses of both a first glass plate and asecond glass plate are thinned, by the use of the interlayer filmaccording to the present invention, the flexural rigidity of laminatedglass can be sufficiently enhanced. In this connection, when thethicknesses of both a first glass plate and a second glass plate arethickened, the flexural rigidity of laminated glass is further enhanced.

Furthermore, since the interlayer film according to the presentinvention is provided with the above-mentioned configuration, the soundinsulating properties of laminated glass prepared with the interlayerfilm can also be enhanced.

It is preferred that a surface at a side opposite to the first layerside of the second layer be a surface on which a lamination glass memberor a glass plate is layered. It is preferred that the thickness of aglass plate to be layered on the second layer be less than 2 mm(preferably 1 mm or less). It is preferred that a surface at a sideopposite to the first layer side of the third layer be a surface onwhich a lamination glass member or a glass plate is layered. It ispreferred that the thickness of a glass plate to be layered on the thirdlayer be less than 2 mm (preferably 1 mm or less).

Since the flexural rigidity can be sufficiently enhanced by virtue ofthe interlayer film, with the use of a first glass plate having athickness of less than 2 mm (preferably 1 mm or less), the interlayerfilm is arranged between the first glass plate and a second glass plateto suitably obtain laminated glass. Since the flexural rigidity can besufficiently enhanced by virtue of the interlayer film, with the use ofa first glass plate having a thickness of less than 2 mm (preferably 1mm or less) and a second glass plate having a thickness of less than 2mm (preferably 1 mm or less), the interlayer film is arranged betweenthe first glass plate and the second glass plate to more suitably obtainlaminated glass.

Hereinafter, specific embodiments of the present invention will bedescribed with reference to the drawings.

FIG. 1 shows an interlayer film for laminated glass in accordance with afirst embodiment of the present invention schematically represented as asectional view.

An interlayer film 11 shown in FIG. 1 is a multi-layered interlayer filmhaving a three or more-layer structure. The interlayer film 11 is usedfor obtaining laminated glass. The interlayer film 11 is an interlayerfilm for laminated glass. The interlayer film 11 is provided with afirst layer 1, a second layer 2, and a third layer 3. The second layer 2is arranged on a first surface 1 a of the first layer 1 to be layeredthereon. The third layer 3 is arranged on a second surface 1 b oppositeto the first surface 1 a of the first layer 1 to be layered thereon. Thefirst layer 1 is an intermediate layer. Each of the second layer 2 andthe third layer 3 is a protective layer and is a surface layer in thepresent embodiment. The first layer 1 is arranged between the secondlayer 2 and the third layer 3 to be sandwiched therebetween.Accordingly, the interlayer film 11 has a multilayer structure (a secondlayer 2/a first layer 1/a third layer 3) in which the second layer 2,the first layer 1, and the third layer 3 are layered in this order.

Hereinafter, the details of the first layer, the second layer and thethird layer which constitute the interlayer film according to thepresent invention, and the details of each ingredient contained in thefirst layer, the second layer and the third layer will be described.

(Polyvinyl Acetal Resin)

The first layer contains a polyvinyl acetal resin (hereinafter,sometimes described as a polyvinyl acetal resin (1)). The second layercontains a polyvinyl acetal resin (hereinafter, sometimes described as apolyvinyl acetal resin (2)). The third layer contains a polyvinyl acetalresin (hereinafter, sometimes described as a polyvinyl acetal resin(3)). Although the polyvinyl acetal resin (1), the polyvinyl acetalresin (2), and the polyvinyl acetal resin (3) may be the same as ordifferent from one another, it is preferred that the polyvinyl acetalresin (1) be different from the polyvinyl acetal resin (2) and thepolyvinyl acetal resin (3) because the sound insulating properties arefurther enhanced. One kind of each of the polyvinyl acetal resin (1),the polyvinyl acetal resin (2), and the polyvinyl acetal resin (3) maybe used alone and two or more kinds thereof may be used in combination.

For example, the polyvinyl acetal resin can be produced by acetalizingpolyvinyl alcohol with an aldehyde. It is preferred that the polyvinylacetal resin be an acetalized product of polyvinyl alcohol. For example,the polyvinyl alcohol can be obtained by saponifying polyvinyl acetate.The saponification degree of the polyvinyl alcohol generally fallswithin the range of 70 to 99.9% by mole.

The average polymerization degree of the polyvinyl alcohol (PVA) ispreferably 200 or more, more preferably 500 or more, even morepreferably 1500 or more, further preferably 1600 or more, especiallypreferably 2600 or more, most preferably 2700 or more, and preferably5000 or less, more preferably 4000 or less and further preferably 3500or less. When the average polymerization degree is the above lower limitor more, the penetration resistance of laminated glass is furtherenhanced. When the average polymerization degree is the above upperlimit or less, formation of an interlayer film is facilitated.

The average polymerization degree of the polyvinyl alcohol is determinedby a method in accordance with JIS K6726 “Testing methods for polyvinylalcohol”.

It is preferred that the number of carbon atoms of the acetal group inthe polyvinyl acetal resin lie within the range of 3 to 5, and it ispreferred that the number of carbon atoms of the acetal group be 4 or 5.

In general, as the aldehyde, an aldehyde with 1 to 10 carbon atoms issuitably used. Examples of the aldehyde with 1 to 10 carbon atomsinclude formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde,isobutyraldehyde, n-valeraldehyde, 2-ethylbutyraldehyde,n-hexylaldehyde, n-octylaldehyde, n-nonylaldehyde, n-decylaldehyde,benzaldehyde, and the like. Of these, acetaldehyde, propionaldehyde,n-butyraldehyde, isobutyraldehyde, n-hexylaldehyde or n-valeraldehyde ispreferred, acetaldehyde, propionaldehyde, n-butyraldehyde,isobutyraldehyde or n-valeraldehyde is more preferred, andn-butyraldehyde or n-valeraldehyde is further preferred. One kind of thealdehyde may be used alone, and two or more kinds thereof may be used incombination.

By making the content of the hydroxyl group of the polyvinyl acetalresin in the first layer lower than the content of the hydroxyl group ofthe polyvinyl acetal resin in the second layer, the sound insulatingproperties of laminated glass can be enhanced. Furthermore, when anabsolute value of a difference between the content of the hydroxyl groupof the polyvinyl acetal resin in the second layer and the content of thehydroxyl group of the polyvinyl acetal resin in the first layer isdefined as XA, by making the absolute value XA 9% by mole or more and11% by mole or less, the flexural rigidity and the sound insulatingproperties of laminated glass can be enhanced. The content of thehydroxyl group of the polyvinyl acetal resin in the first layer ispreferably lower by 12% by mole or more, more preferably lower by 13% bymole or more, and further preferably lower by 14% by mole or more, thanthe content of the hydroxyl group of the polyvinyl acetal resin in thesecond layer. The preferred lower limit of the absolute value XA is 6%by mole, the more preferred lower limit thereof is 7% by mole, thefurther preferred lower limit thereof is 8% by mole, the preferred upperlimit thereof is 14% by mole, the more preferred upper limit thereof is13% by mole, and the further preferred upper limit thereof is 12% bymole.

By making the content of the hydroxyl group of the polyvinyl acetalresin in the first layer lower than the content of the hydroxyl group ofthe polyvinyl acetal resin in the third layer, the sound insulatingproperties of laminated glass can be enhanced. Furthermore, when anabsolute value of a difference between the content of the hydroxyl groupof the polyvinyl acetal resin in the third layer and the content of thehydroxyl group of the polyvinyl acetal resin in the first layer isdefined as XB, by making the absolute value XB 9% by mole or more and11% by mole or less, the flexural rigidity and the sound insulatingproperties of laminated glass can be enhanced. The content of thehydroxyl group of the polyvinyl acetal resin in the first layer ispreferably lower by 12% by mole or more, more preferably lower by 13% bymole or more, and further preferably lower by 14% by mole or more, thanthe content of the hydroxyl group of the polyvinyl acetal resin in thethird layer. The preferred lower limit of the absolute value XB is 6% bymole, the more preferred lower limit thereof is 7% by mole, the furtherpreferred lower limit thereof is 8% by mole, the preferred upper limitthereof is 14% by mole, the more preferred upper limit thereof is 13% bymole, and the further preferred upper limit thereof is 12% by mole.

The content of the hydroxyl group (the amount of hydroxyl groups) of thepolyvinyl acetal resin (1) is preferably 17% by mole or more, morepreferably 20% by mole or more, further preferably 22% by mole or more,and preferably 28% by mole or less, more preferably 27% by mole or less,further preferably 25% by mole or less, and especially preferably 24% bymole or less. When the content of the hydroxyl group is the above lowerlimit or more, the mechanical strength of the interlayer film is furtherenhanced. In particular, when the content of the hydroxyl group of thepolyvinyl acetal resin (1) is 20% by mole or more, the resin is high inreaction efficiency and is excellent in productivity, and moreover, whenbeing 28% by mole or less, the sound insulating properties of laminatedglass are further enhanced. Moreover, when the content of the hydroxylgroup is the above upper limit or less, the flexibility of theinterlayer film is enhanced and the handling of the interlayer film isfacilitated.

The content of the hydroxyl group of each of the polyvinyl acetal resin(2) and the polyvinyl acetal resin (3) is preferably 25% by mole ormore, more preferably 28% by mole or more, more preferably 30% by moleor more, even more preferably 31.5% by mole or more, further preferably32% by mole or more, especially preferably 33% by mole or more, andpreferably 40% by mole or less, more preferably 38% by mole or less,further preferably 37% by mole or less, and especially preferably 36% bymole or less. When the content of the hydroxyl group is the above lowerlimit or more, the flexural rigidity is further enhanced and theadhesive force of the interlayer film is further enhanced. Moreover,when the content of the hydroxyl group is the above upper limit or less,the flexibility of the interlayer film is enhanced and the handling ofthe interlayer film is facilitated.

From the viewpoint of still further enhancing the sound insulatingproperties, each of the absolute value of the difference between thecontent of the hydroxyl group of the polyvinyl acetal resin (1) and thecontent of the hydroxyl group of the polyvinyl acetal resin (2) and theabsolute value of the difference between the content of the hydroxylgroup of the polyvinyl acetal resin (1) and the content of the hydroxylgroup of the polyvinyl acetal resin (3) is preferably 1% by mole ormore, more preferably 5% by mole or more, further preferably 9% by moleor more, especially preferably 10% by mole or more, and most preferably12% by mole or more. Each of the absolute value of the differencebetween the content of the hydroxyl group of the polyvinyl acetal resin(1) and the content of the hydroxyl group of the polyvinyl acetal resin(2) and the absolute value of the difference between the content of thehydroxyl group of the polyvinyl acetal resin (1) and the content of thehydroxyl group of the polyvinyl acetal resin (3) is preferably 20% bymole or less.

The content of the hydroxyl group of the polyvinyl acetal resin is amole fraction, represented in percentage, obtained by dividing theamount of ethylene groups to which the hydroxyl group is bonded by thetotal amount of ethylene groups in the main chain. For example, theamount of ethylene groups to which the hydroxyl group is bonded can bemeasured in accordance with JIS K6728 “Testing methods for polyvinylbutyral”.

The acetylation degree (the amount of acetyl groups) of the polyvinylacetal resin (1) is preferably 0.01% by mole or more, more preferably0.1% by mole or more, even more preferably 7% by mole or more, furtherpreferably 9% by mole or more, and preferably 30% by mole or less, morepreferably 25% by mole or less, further preferably 24% by mole or less,and especially preferably 20% by mole or less. When the acetylationdegree is the above lower limit or more, the compatibility between thepolyvinyl acetal resin and a plasticizer is enhanced. When theacetylation degree is the above upper limit or less, with regard to theinterlayer film and laminated glass, the moisture resistance thereof isenhanced. In particular, when the acetylation degree of the polyvinylacetal resin (1) is 0.1% by mole or more and 25% by mole or less, theresulting laminated glass is excellent in penetration resistance.

The acetylation degree of each of the polyvinyl acetal resin (2) and thepolyvinyl acetal resin (3) is preferably 0.01% by mole or more, morepreferably 0.5% by mole or more, and preferably 10% by mole or less, andmore preferably 2% by mole or less. When the acetylation degree is theabove lower limit or more, the compatibility between the polyvinylacetal resin and a plasticizer is enhanced. When the acetylation degreeis the above upper limit or less, with regard to the interlayer film andlaminated glass, the moisture resistance thereof is enhanced.

The acetylation degree is a mole fraction, represented in percentage,obtained by dividing the amount of ethylene groups to which the acetylgroup is bonded by the total amount of ethylene groups in the mainchain. For example, the amount of ethylene groups to which the acetylgroup is bonded can be measured in accordance with JIS K6728 “Testingmethods for polyvinyl butyral”.

The acetalization degree of the polyvinyl acetal resin (1) (thebutyralization degree in the case of a polyvinyl butyral resin) ispreferably 47% by mole or more, more preferably 60% by mole or more, andpreferably 85% by mole or less, more preferably 80% by mole or less, andfurther preferably 75% by mole or less. When the acetalization degree isthe above lower limit or more, the compatibility between the polyvinylacetal resin and a plasticizer is enhanced. When the acetalizationdegree is the above upper limit or less, the reaction time required forproducing the polyvinyl acetal resin is shortened.

The acetalization degree of each of the polyvinyl acetal resin (2) andthe polyvinyl acetal resin (3) (the butyralization degree in the case ofa polyvinyl butyral resin) is preferably 55% by mole or more, morepreferably 60% by mole or more, and preferably 75% by mole or less andmore preferably 71% by mole or less. When the acetalization degree isthe above lower limit or more, the compatibility between the polyvinylacetal resin and a plasticizer is enhanced. When the acetalizationdegree is the above upper limit or less, the reaction time required forproducing the polyvinyl acetal resin is shortened.

The acetalization degree is a mole fraction, represented in percentage,obtained by dividing a value obtained by subtracting the amount ofethylene groups to which the hydroxyl group is bonded and the amount ofethylene groups to which the acetyl group is bonded from the totalamount of ethylene groups in the main chain by the total amount ofethylene groups in the main chain.

In this connection, it is preferred that the content of the hydroxylgroup (the amount of hydroxyl groups), the acetalization degree (thebutyralization degree) and the acetylation degree be calculated from theresults measured by a method in accordance with JIS K6728 “Testingmethods for polyvinyl butyral”. In this context, a method in accordancewith ASTM D1396-92 may be used. When the polyvinyl acetal resin is apolyvinyl butyral resin, the content of the hydroxyl group (the amountof hydroxyl groups), the acetalization degree (the butyralizationdegree) and the acetylation degree can be calculated from the resultsmeasured by a method in accordance with JIS K6728 “Testing methods forpolyvinyl butyral”.

From the viewpoint of further improving the penetration resistance oflaminated glass, it is preferred that the polyvinyl acetal resin (1) bea polyvinyl acetal resin (A) with an acetylation degree (a) of less than8% by mole and an acetalization degree (a) of 65% by mole or more or apolyvinyl acetal resin (B) with an acetylation degree (b) of 8% by moleor more. Each of the polyvinyl acetal resin (2) and the polyvinyl acetalresin (3) may be the polyvinyl acetal resin (A) and may be the polyvinylacetal resin (B).

The acetylation degree (a) of the polyvinyl acetal resin (A) is lessthan 8% by mole, preferably 7.9% by mole or less, more preferably 7.8%by mole or less, further preferably 6.5% by mole or less, especiallypreferably 6% by mole or less, and preferably 0.1% by mole or more, morepreferably 0.5% by mole or more, further preferably 2% by mole or more,especially preferably 5% by mole or more, and most preferably 5.5% bymole or more. When the acetylation degree (a) is 0.1% by mole or moreand less than 8% by mole, the transfer of a plasticizer can be easilycontrolled and the sound insulating properties of laminated glass arefurther enhanced.

The acetalization degree (a) of the polyvinyl acetal resin (A) is 65% bymole or more, preferably 66% by mole or more, more preferably 67% bymole or more, further preferably 67.5% by mole or more, especiallypreferably 75% by mole or more, and preferably 85% by mole or less, morepreferably 84% by mole or less, further preferably 83% by mole or lessand especially preferably 82% by mole or less. When the acetalizationdegree (a) is the above lower limit or more, the sound insulatingproperties of laminated glass are further enhanced. When theacetalization degree (a) is the above upper limit or less, the reactiontime required for producing the polyvinyl acetal resin (A) can beshortened.

The content (a) of the hydroxyl group of the polyvinyl acetal resin (A)is preferably 18% by mole or more, more preferably 19% by mole or more,further preferably 20% by mole or more, especially preferably 21% bymole or more, most preferably 23% by mole or more, and preferably 31% bymole or less, more preferably 30% by mole or less, further preferably29% by mole or less, and especially preferably 28% by mole or less. Whenthe content (a) of the hydroxyl group is the above lower limit or more,the adhesive force of the first layer is further enhanced. When thecontent (a) of the hydroxyl group is the above upper limit or less, thesound insulating properties of laminated glass are further enhanced.

The acetylation degree (b) of the polyvinyl acetal resin (B) is 8% bymole or more, preferably 9% by mole or more, more preferably 9.5% bymole or more, further preferably 10% by mole or more, especiallypreferably 10.5% by mole or more, and preferably 30% by mole or less,more preferably 28% by mole or less, further preferably 26% by mole orless and especially preferably 24% by mole or less. When the acetylationdegree (b) is the above lower limit or more, the sound insulatingproperties of laminated glass are further enhanced. When the acetylationdegree (b) is the above upper limit or less, the reaction time requiredfor producing the polyvinyl acetal resin (B) can be shortened.

The acetalization degree (b) of the polyvinyl acetal resin (B) ispreferably 50% by mole or more, more preferably 53% by mole or more,further preferably 55% by mole or more, especially preferably 60% bymole or more, and preferably 78% by mole or less, more preferably 75% bymole or less, further preferably 72% by mole or less and especiallypreferably 70% by mole or less. When the acetalization degree (b) is theabove lower limit or more, the sound insulating properties of laminatedglass are further enhanced. When the acetalization degree (b) is theabove upper limit or less, the reaction time required for producing thepolyvinyl acetal resin (B) can be shortened.

The content (b) of the hydroxyl group of the polyvinyl acetal resin (B)is preferably 18% by mole or more, more preferably 19% by mole or more,further preferably 20% by mole or more, especially preferably 21% bymole or more, most preferably 23% by mole or more, and preferably 31% bymole or less, more preferably 30% by mole or less, further preferably29% by mole or less, and especially preferably 28% by mole or less. Whenthe content (b) of the hydroxyl group is the above lower limit or more,the adhesive force of the first layer is further enhanced. When thecontent (b) of the hydroxyl group is the above upper limit or less, thesound insulating properties of laminated glass are further enhanced.

It is preferred that each of the polyvinyl acetal resin (A) and thepolyvinyl acetal resin (B) be a polyvinyl butyral resin.

(Plasticizer)

The first layer contains a plasticizer (hereinafter, sometimes describedas a plasticizer (1)). The second layer contains a plasticizer(hereinafter, sometimes described as a plasticizer (2)). The third layercontains a plasticizer (hereinafter, sometimes described as aplasticizer (3)). By using a polyvinyl acetal resin and a plasticizertogether, the adhesive force of a layer containing the polyvinyl acetalresin and the plasticizer to a lamination glass member or another layeris moderately enhanced. The plasticizer is not particularly limited. Theplasticizer (1), the plasticizer (2), and the plasticizer (3) may be thesame as or different from one another. One kind of each of theplasticizer (1), the plasticizer (2), and the plasticizer (3) may beused alone and two or more kinds thereof may be used in combination.

Examples of the plasticizer include organic ester plasticizers such as amonobasic organic acid ester and a polybasic organic acid ester, organicphosphate plasticizers such as an organic phosphate plasticizer and anorganic phosphite plasticizer, and the like. Of these, organic esterplasticizers are preferred. It is preferred that the plasticizer be aliquid plasticizer.

Examples of the monobasic organic acid ester include a glycol esterobtained by the reaction of a glycol with a monobasic organic acid, andthe like. Examples of the glycol include triethylene glycol,tetraethylene glycol, tripropylene glycol, and the like. Examples of themonobasic organic acid include butyric acid, isobutyric acid, caproicacid, 2-ethylbutyric acid, heptanoic acid, n-octylic acid,2-ethylhexanoic acid, n-nonylic acid, decanoic acid, and the like.

Examples of the polybasic organic acid ester include an ester compoundof a polybasic organic acid and an alcohol having a linear or branchedstructure of 4 to 8 carbon atoms. Examples of the polybasic organic acidinclude adipic acid, sebacic acid, azelaic acid, and the like.

Examples of the organic ester plasticizer include triethylene glycoldi-2-ethylpropanoate, triethylene glycol di-2-ethylbutyrate, triethyleneglycol di-2-ethylhexanoate, triethylene glycol dicaprylate, triethyleneglycol di-n-octanoate, triethylene glycol di-n-heptanoate, tetraethyleneglycol di-n-heptanoate, dibutyl sebacate, dioctyl azelate, dibutylcarbitol adipate, ethylene glycol di-2-ethylbutyrate, 1,3-propyleneglycol di-2-ethylbutyrate, 1,4-butylene glycol di-2-ethylbutyrate,diethylene glycol di-2-ethylbutyrate, diethylene glycoldi-2-ethylhexanoate, dipropylene glycol di-2-ethylbutyrate, triethyleneglycol di-2-ethylpentanoate, tetraethylene glycol di-2-ethylbutyrate,diethylene glycol dicaprylate, dihexyl adipate, dioctyl adipate, hexylcyclohexyl adipate, a mixture of heptyl adipate and nonyl adipate,diisononyl adipate, diisodecyl adipate, heptyl nonyl adipate, dibutylsebacate, oil-modified sebacic alkyds, a mixture of a phosphoric acidester and an adipic acid ester, and the like. Organic ester plasticizersother than these may be used. Other adipic acid esters other than theabove-described adipic acid esters may be used.

Examples of the organic phosphate plasticizer include tributoxyethylphosphate, isodecyl phenyl phosphate, triisopropyl phosphate, and thelike.

It is preferred that the plasticizer be a diester plasticizerrepresented by the following formula (1).

In the foregoing formula (1), R1 and R2 each represent an organic groupwith 2 to 10 carbon atoms, R3 represents an ethylene group, anisopropylene group or an n-propylene group, and p represents an integerof 3 to 10. It is preferred that R1 and R2 in the foregoing formula (1)each be an organic group with 5 to 10 carbon atoms, and it is morepreferred that R1 and R2 each be an organic group with 6 to 10 carbonatoms.

It is preferred that the plasticizer include di-(2-butoxyethyl)-adipate(DBEA), triethylene glycol di-2-ethylhexanoate (3GO), triethylene glycoldi-2-ethylbutyrate (3GH), or triethylene glycol di-2-ethylpropanoate, itis more preferred that the plasticizer include triethylene glycoldi-2-ethylhexanoate (3GO), triethylene glycol di-2-ethylbutyrate (3GH),or triethylene glycol di-2-ethylpropanoate, it is further preferred thatthe plasticizer include triethylene glycol di-2-ethylhexanoate ortriethylene glycol di-2-ethylbutyrate, and it is especially preferredthat the plasticizer include triethylene glycol di-2-ethylhexanoate.

Each of the content of the plasticizer (2) (hereinafter, sometimesdescribed as the content (2)) relative to 100 parts by weight of thepolyvinyl acetal resin (2) and the content of the plasticizer (3)(hereinafter, sometimes described as the content (3)) relative to 100parts by weight of the polyvinyl acetal resin (3) is preferably 10 partsby weight or more, more preferably 15 parts by weight or more, furtherpreferably 20 parts by weight or more, especially preferably 24 parts byweight or more, preferably 50 parts by weight or less, more preferably40 parts by weight or less, further preferably 35 parts by weight orless, especially preferably 32 parts by weight or less, and mostpreferably 30 parts by weight or less. When the content (2) and thecontent (3) are the above lower limit or more, the flexibility of theinterlayer film is enhanced and the handling of the interlayer film isfacilitated. When the content (2) and the content (3) are the aboveupper limit or less, the flexural rigidity is further enhanced.

The content of the plasticizer (1) (hereinafter, sometimes described asthe content (1)) relative to 100 parts by weight of the polyvinyl acetalresin (1) is preferably 50 parts by weight or more, more preferably 55parts by weight or more, further preferably 60 parts by weight or more,preferably 100 parts by weight or less, more preferably 90 parts byweight or less, further preferably 85 parts by weight or less, andespecially preferably 80 parts by weight or less. When the content (1)is the above lower limit or more, the flexibility of the interlayer filmis enhanced and the handling of the interlayer film is facilitated. Whenthe content (1) is the above upper limit or less, the penetrationresistance of laminated glass is further enhanced.

For the purpose of enhancing the sound insulating properties oflaminated glass, it is preferred that the content (1) be larger than thecontent (2) and it is preferred that the content (1) be larger than thecontent (3).

In particular, from the viewpoint of further enhancing the soundinsulating properties of laminated glass, each of the absolute value ofthe difference between the content (2) and the content (1) and theabsolute value of the difference between the content (3) and the content(1) is preferably 10 parts by weight or more, more preferably 15 partsby weight or more, and further preferably 20 parts by weight or more.Each of the absolute value of the difference between the content (2) andthe content (1) and the absolute value of the difference between thecontent (3) and the content (1) is preferably 80 parts by weight orless, more preferably 75 parts by weight or less, and further preferably70 parts by weight or less.

Furthermore, the content Y is preferably 25 parts by weight or more,more preferably 26 parts by weight or more, and further preferably 27parts by weight or more because the sound insulating properties oflaminated glass are further enhanced. The content Y is preferably 41parts by weight or less, more preferably 40.5 parts by weight or less,and further preferably 40 parts by weight or less because the rigidityof laminated glass is further enhanced.

A conventional sound insulating film has a layered structure with astack of a surface layer, a sound insulating layer, and a surface layerand the sound insulating layer is softer than the surface layer.Laminated glass prepared with such a sound insulating film is made lowin rigidity. In order to prevent laminated glass from being made low inrigidity due to the sound insulating layer, US 2013/0236711 A1 disclosesa technique for making a surface layer have a high glass transitiontemperature. However, only by making a surface layer have a high glasstransition temperature, sufficient rigidity of laminated glassimmediately after the preparation fails to be attained, and in addition,there is a problem that the rigidity of laminated glass is significantlylowered when a certain period of time has elapsed from the preparation.On the other hand, when a sound insulating layer is made harder, thereis a problem that sufficient sound insulating properties fail to beattained. On that account, as a result of researches on the cause ofthese problems, the present inventors found out that these problems areattributed to the transfer of a plasticizer contained in the surfacelayer or the sound insulating layer. That is, the rigidity not only oflaminated glass immediately after the preparation but also of laminatedglass after a certain period of time has elapsed from the preparationcan be enhanced as long as a plasticizer contained in the surface layercan be prevented from excessively transferring to the sound insulatinglayer and a plasticizer contained in the sound insulating layer can beprevented from excessively transferring to the surface layer.

A concrete means for solving these problems will be described. By makingthe content of the hydroxyl group of the polyvinyl acetal resin in thefirst layer lower than the content of the hydroxyl group of thepolyvinyl acetal resin in the second layer and making the content of thehydroxyl group of the polyvinyl acetal resin in the first layer lowerthan the content of the hydroxyl group of the polyvinyl acetal resin inthe third layer, the sound insulating properties of laminated glass areenhanced. However, the plasticizer in the second layer and theplasticizer in the third layer have a tendency to transfer into thefirst layer. When the transfer of the plasticizer progresses excessivelywith the lapse of time, the first layer becomes soft and the flexuralrigidity of laminated glass is lowered. Furthermore, the soundinsulating properties of laminated glass can be enhanced by making thelower limit of each of the absolute value XA of a difference between thecontent of the hydroxyl group of the polyvinyl acetal resin in the firstlayer and the content of the hydroxyl group of the polyvinyl acetalresin in the second layer and the absolute value XB of a differencebetween the content of the hydroxyl group of the polyvinyl acetal resinin the first layer and the content of the hydroxyl group of thepolyvinyl acetal resin in the third layer 6% by mole, and the flexuralrigidity of laminated glass can be enhanced by making the upper limitthereof 14% by mole. The preferred lower limit of each of the absolutevalue XA and the absolute value XB is 7% by mole, the more preferredlower limit thereof is 8% by mole, the further preferred lower limitthereof is 9% by mole, the preferred upper limit thereof is 13% by mole,the more preferred upper limit thereof is 12% by mole, and the furtherpreferred upper limit thereof is 11% by mole.

Furthermore, when a content of the plasticizer in the interlayer filmfor laminated glass relative to 100 parts by weight of the polyvinylacetal resin in the interlayer film for laminated glass is defined as Y,XA, XB, and Y satisfy the equations of Y≤−1.68XA+56 and Y≤−1.68XB+56.The plasticizer in the second layer and the plasticizer in the thirdlayer have a tendency to transfer into the first layer as the absolutevalue XA and the absolute value XB become large. On that account, evenif the absolute value XA and the absolute value XB become large, bydecreasing the content Y of the plasticizer in the interlayer film forlaminated glass relative to 100 parts by weight of the polyvinyl acetalresin in the interlayer film for laminated glass, namely, the totalnumerical value of parts of the plasticizer in the interlayer film forlaminated glass, the rigidity not only of laminated glass immediatelyafter the preparation but also of laminated glass after a certain periodof time has elapsed from the preparation can be enhanced. On the otherhand, the plasticizer in the second layer and the plasticizer in thethird layer have a tendency not to transfer into the first layer as theabsolute value XA and the absolute value XB become small. On thataccount, even if the absolute value XA and the absolute value XB becomesmall, by increasing the content Y of the plasticizer in the interlayerfilm for laminated glass relative to 100 parts by weight of thepolyvinyl acetal resin in the interlayer film for laminated glass,namely, the total numerical value of parts of the plasticizer in theinterlayer film for laminated glass, the sound insulating properties oflaminated glass can be enhanced.

The content Y and XA preferably satisfy the equation of Y≤−1.68XA+56,more preferably satisfy the equation of Y≤−1.68XA+55.5 and furtherpreferably satisfy the equation of Y≤−1.68XA+55, because the rigidity oflaminated glass is further enhanced. The content Y and XA preferablysatisfy the equation of Y≥−1.68XA+47, more preferably satisfy theequation of Y≥−1.68XA+48, further preferably satisfy the equation ofY≥−1.68XA+49, and especially preferably satisfy the equation ofY≤−1.68XA+50, because the sound insulating properties of laminated glassare further enhanced. The content Y and XB preferably satisfy theequation of Y≤−1.68XB+56, more preferably satisfy the equation ofY≤−1.68XB+55.5 and further preferably satisfy the equation ofY≤−1.68XB+55, because the rigidity of laminated glass is furtherenhanced. The content Y and XB preferably satisfy the equation ofY≥−1.68XB+47, more preferably satisfy the equation of Y≥−1.68XB+48,further preferably satisfy the equation of Y≥−1.68XB+49, and especiallypreferably satisfy the equation of Y≤−1.68XB+50, because the soundinsulating properties of laminated glass are further enhanced.

In this context, the content Y of the plasticizer in the interlayer filmfor laminated glass relative to 100 parts by weight of the polyvinylacetal resin in the interlayer film for laminated glass will bedescribed. An interlayer film for laminated glass is cut into a size of0.5 cm in longitudinal length by 5 cm in transversal length, and in thecase of the three-layer structure with a stack of the second layer, thefirst layer, and the third layer, the interlayer film for laminatedglass is allowed to stand for 12 hours under an environment of 23±2° C.and a humidity of 25±5%, after which the second layer is peeled off fromthe first layer, and then, the third layer is peeled off from the firstlayer. The weight of the peeled first layer is measured with the use ofan electronic balance for analysis (GH-200 available from A&D Company,Limited) and the weight of the peeled first layer is defined as X1 (mg).With the use of a gas chromatograph (GC-2014 available from SHIMADZUCORPORATION), the peeled first layer is measured for the percentagecontent (R1) occupied by the polyvinyl acetal resin in the total of thepolyvinyl acetal resin and the plasticizer contained in the first layerand the percentage content (P1) occupied by the plasticizer in the totalof the polyvinyl acetal resin and the plasticizer contained in the firstlayer. In this connection, R1 mentioned above is calculated by dividingthe content of the thermoplastic resin in the first layer by the totalcontent of the polyvinyl acetal resin and the plasticizer in the firstlayer and P1 mentioned above is calculated by dividing the content ofthe plasticizer in the first layer by the total content of the polyvinylacetal resin and the plasticizer in the first layer. Similarly, theweight X2 (mg) of the second layer, the percentage content (R2) occupiedby the polyvinyl acetal resin in the total of the polyvinyl acetal resinand the plasticizer contained in the second layer, and the percentagecontent (P2) occupied by the plasticizer in the total of the polyvinylacetal resin and the plasticizer contained in the second layer aremeasured. Similarly, the weight X3 (mg) of the third layer, thepercentage content (R3) occupied by the polyvinyl acetal resin in thetotal of the polyvinyl acetal resin and the plasticizer contained in thethird layer, and the percentage content (P3) occupied by the plasticizerin the total of the polyvinyl acetal resin and the plasticizer containedin the third layer are measured. Furthermore, the content of thepolyvinyl acetal resin in the first layer is calculated as X1 (mg)×R1,the content of the polyvinyl acetal resin in the second layer iscalculated as X2 (mg)×R2, the content of the polyvinyl acetal resin inthe third layer is calculated as X3 (mg)×R3, and the content of thepolyvinyl acetal resin in the interlayer film for laminated glass isdefined as X1 (mg)×R1+X2 (mg)×R2+X3 (mg)×R3. Similarly, the content ofthe plasticizer in the first layer is calculated as X1 (mg)×P1, thecontent of the plasticizer in the second layer is calculated as X2(mg)×P2, the content of the plasticizer in the third layer is calculatedas X3 (mg)×P3, and the content of the plasticizer in the interlayer filmfor laminated glass is defined as X1 (mg)×P1+X2 (mg)×P2+X3 (mg)×P3. Fromthese results, the content Y of the plasticizer in the interlayer filmfor laminated glass relative to 100 parts by weight of the polyvinylacetal resin in the interlayer film for laminated glass is calculated as[{X1 (mg)×P1+X2 (mg)×P2+X3 (mg)×P3}/{X1 (mg)×R1+X2 (mg)×R2+X3 (mg)×R3}].When the interlayer film for laminated glass has a four or more-layermultilayer structure, it is preferred that the first layer, the secondlayer, and the third layer be specified to measure the content Y of theplasticizer in the interlayer film for laminated glass relative to 100parts by weight of the polyvinyl acetal resin in the interlayer film forlaminated glass as in the case of an interlayer film having athree-layer structure. In this connection, when at least one layer ofthe first layer, the second layer, and the third layer has a coloredregion and the colored region exists only on an area extending along thein-plane direction of an interlayer film for laminated glass, it ispreferred that the interlayer film for laminated glass be cut into asize of 0.5 cm in longitudinal length by 5 cm in transversal length soas not to include the colored region, and then, the content Y of theplasticizer in the interlayer film for laminated glass relative to 100parts by weight of the polyvinyl acetal resin in the interlayer film forlaminated glass be measured.

(Silica Particles)

It is preferred that the first layer contains silica particles. By theuse of silica particles, without lowering the sound insulatingproperties, the rigidity is further enhanced, and furthermore, theadhesive force between respective layers is also enhanced. One kind ofthe silica particle may be used alone and two or more kinds thereof maybe used in combination.

The specific surface area by the BET method of the silica particle ispreferably 50 m²/g or more, more preferably 100 m²/g or more, furtherpreferably 200 m²/g or more, especially preferably 250 m²/g or more,most preferably 300 m²/g or more, and preferably 500 m²/g or less. Thespecific surface area can be measured by a gas adsorption method using aspecific surface area/fine pore distribution measuring apparatus.Examples of the measuring apparatus include “ASAP 2420” available fromSHIMADZU CORPORATION, and the like.

Relative to 100 parts by weight of the polyvinyl acetal resin (1), thecontent of the silica particle is preferably 1 part by weight or more,more preferably 5 parts by weight or more, further preferably 10 partsby weight or more, especially preferably 15 parts by weight or more, andpreferably 70 parts by weight or less, more preferably 64 parts byweight or less, even more preferably 60 parts by weight or less, furtherpreferably 55 parts by weight or less, especially preferably 45 parts byweight or less, and most preferably 35 parts by weight or less. When thecontent of the silica particle is the above lower limit or more, theadhesive force between respective layers is further enhanced and therigidity is further enhanced. When the content of the silica particle isthe above upper limit or less, the sound insulating properties arefurther enhanced.

(Heat Shielding Compound)

It is preferred that the interlayer film include a heat shieldingcompound. It is preferred that the first layer contain a heat shieldingcompound. It is preferred that the second layer contain a heat shieldingcompound. It is preferred that the third layer contain a heat shieldingcompound. One kind of the heat shielding compound may be used alone, andtwo or more kinds thereof may be used in combination.

Ingredient X:

It is preferred that the interlayer film include at least one kind ofIngredient X among a phthalocyanine compound, a naphthalocyaninecompound and an anthracyanine compound. It is preferred that the firstlayer contain the Ingredient X. It is preferred that the second layercontain the Ingredient X. It is preferred that the third layer containthe Ingredient X. The Ingredient X is a heat shielding compound. Onekind of the Ingredient X may be used alone, and two or more kindsthereof may be used in combination.

The Ingredient X is not particularly limited. As the Ingredient X,conventionally known phthalocyanine compound, naphthalocyanine compoundand anthracyanine compound can be used.

With regard to the interlayer film and laminated glass, from theviewpoint of further enhancing the heat shielding properties thereof, itis preferred that the Ingredient X be at least one kind selected fromthe group consisting of phthalocyanine, a derivative of phthalocyanine,naphthalocyanine and a derivative of naphthalocyanine, and it is morepreferred that the Ingredient X be at least one kind amongphthalocyanine and a derivative of phthalocyanine.

From the viewpoints of effectively enhancing the heat shieldingproperties and maintaining the visible light transmittance at a higherlevel over a long period of time, it is preferred that the Ingredient Xcontain vanadium atoms or copper atoms. It is preferred that theIngredient X contain vanadium atoms and it is also preferred that theIngredient X contain copper atoms. It is more preferred that theIngredient X be at least one kind among phthalocyanine containingvanadium atoms or copper atoms and a derivative of phthalocyaninecontaining vanadium atoms or copper atoms. With regard to the interlayerfilm and laminated glass, from the viewpoint of still further enhancingthe heat shielding properties thereof, it is preferred that theIngredient X have a structural unit in which an oxygen atom is bonded toa vanadium atom.

In 100% by weight of a layer containing the Ingredient X (a first layer,a second layer or a third layer), the content of the Ingredient X ispreferably 0.001% by weight or more, more preferably 0.005% by weight ormore, further preferably 0.01% by weight or more, especially preferably0.02% by weight or more, and preferably 0.2% by weight or less, morepreferably 0.1% by weight or less, further preferably 0.05% by weight orless and especially preferably 0.04% by weight or less. When the contentof the Ingredient X is the above lower limit or more and the above upperlimit or less, the heat shielding properties are sufficiently enhancedand the visible light transmittance is sufficiently enhanced. Forexample, it is possible to make the visible light transmittance 70% ormore.

Heat Shielding Particles:

It is preferred that the interlayer film include heat shieldingparticles. It is preferred that the first layer contain the heatshielding particles. It is preferred that the second layer contain theheat shielding particles. It is preferred that the third layer containthe heat shielding particles. The heat shielding particle is of a heatshielding compound. By the use of heat shielding particles, infraredrays (heat rays) can be effectively cut off. One kind of the heatshielding particles may be used alone, and two or more kinds thereof maybe used in combination.

From the viewpoint of further enhancing the heat shielding properties oflaminated glass, it is more preferred that the heat shielding particlesbe metal oxide particles. It is preferred that the heat shieldingparticle be a particle (a metal oxide particle) formed from an oxide ofa metal.

The energy amount of an infrared ray with a wavelength of 780 nm orlonger which is longer than that of visible light is small as comparedwith an ultraviolet ray. However, the thermal action of infrared rays islarge, and when infrared rays are absorbed into a substance, heat isreleased from the substance. As such, infrared rays are generally calledheat rays. By the use of the heat shielding particles, infrared rays(heat rays) can be effectively cut off. In this connection, the heatshielding particle means a particle capable of absorbing infrared rays.

Specific examples of the heat shielding particles include metal oxideparticles such as aluminum-doped tin oxide particles, indium-doped tinoxide particles, antimony-doped tin oxide particles (ATO particles),gallium-doped zinc oxide particles (GZO particles), indium-doped zincoxide particles (IZO particles), aluminum-doped zinc oxide particles(AZO particles), niobium-doped titanium oxide particles, sodium-dopedtungsten oxide particles, cesium-doped tungsten oxide particles,thallium-doped tungsten oxide particles, rubidium-doped tungsten oxideparticles, tin-doped indium oxide particles (ITO particles), tin-dopedzinc oxide particles and silicon-doped zinc oxide particles, lanthanumhexaboride (LaB₆) particles, and the like. Heat shielding particlesother than these may be used. Of these, since the heat ray shieldingfunction is high, preferred are metal oxide particles, more preferredare ATO particles, GZO particles, IZO particles, ITO particles ortungsten oxide particles, and especially preferred are ITO particles ortungsten oxide particles. In particular, since the heat ray shieldingfunction is high and the particles are readily available, preferred aretin-doped indium oxide particles (ITO particles), and also preferred aretungsten oxide particles.

With regard to the interlayer film and laminated glass, from theviewpoint of further enhancing the heat shielding properties thereof, itis preferred that the tungsten oxide particles be metal-doped tungstenoxide particles. Examples of the “tungsten oxide particles” includemetal-doped tungsten oxide particles. Specifically, examples of themetal-doped tungsten oxide particles include sodium-doped tungsten oxideparticles, cesium-doped tungsten oxide particles, thallium-dopedtungsten oxide particles, rubidium-doped tungsten oxide particles, andthe like.

With regard to the interlayer film and laminated glass, from theviewpoint of further enhancing the heat shielding properties thereof,cesium-doped tungsten oxide particles are especially preferred. Withregard to the interlayer film and laminated glass, from the viewpoint ofstill further enhancing the heat shielding properties thereof, it ispreferred that the cesium-doped tungsten oxide particles be tungstenoxide particles represented by the formula: Cs_(0.33)WO₃.

The average particle diameter of the heat shielding particles ispreferably 0.01 μm or more, more preferably 0.02 μm or more, andpreferably 0.1 μm or less and more preferably 0.05 μm or less. When theaverage particle diameter is the above lower limit or more, the heat rayshielding properties are sufficiently enhanced. When the averageparticle diameter is the above upper limit or less, the dispersibilityof heat shielding particles is enhanced.

The “average particle diameter” refers to the volume average particlediameter. The average particle diameter can be measured using a particlesize distribution measuring apparatus (“UPA-EX150” available fromNIKKISO CO., LTD.), or the like.

In 100% by weight of a layer containing the heat shielding particles (afirst layer, a second layer or a third layer), each content of the heatshielding particles is preferably 0.01% by weight or more, morepreferably 0.1% by weight or more, further preferably 1% by weight ormore, especially preferably 1.5% by weight or more, and preferably 6% byweight or less, more preferably 5.5% by weight or less, furtherpreferably 4% by weight or less, especially preferably 3.5% by weight orless and most preferably 3% by weight or less. When the content of theheat shielding particles is the above lower limit or more and the aboveupper limit or less, the heat shielding properties are sufficientlyenhanced and the visible light transmittance is sufficiently enhanced.

(Metal Salt)

It is preferred that the interlayer film include at least one kind ofmetal salt (hereinafter, sometimes described as Metal salt M) among analkali metal salt, an alkaline earth metal salt, and an Mg salt. It ispreferred that the first layer contain the Metal salt M. It is preferredthat the second layer contain the Metal salt M. It is preferred that thethird layer contain the Metal salt M. By the use of the Metal salt M,controlling the adhesivity between the interlayer film and a laminationglass member or the adhesivity between respective layers in theinterlayer film is facilitated. One kind of the Metal salt M may be usedalone and two or more kinds thereof may be used in combination.

It is preferred that the Metal salt M contain at least one kind of metalselected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, andBa. It is preferred that the metal salt contained in the interlayer filmcontain at least one kind of metal between K and Mg.

Moreover, it is more preferred that the Metal salt M be an alkali metalsalt of an organic acid with 2 to 16 carbon atoms, an alkaline earthmetal salt of an organic acid with 2 to 16 carbon atoms, and a magnesiumsalt of an organic acid with 2 to 16 carbon atoms, and it is furtherpreferred that the Metal salt M be a magnesium carboxylate with 2 to 16carbon atoms or a potassium carboxylate with 2 to 16 carbon atoms.

Although the magnesium carboxylate with 2 to 16 carbon atoms and thepotassium carboxylate with 2 to 16 carbon atoms are not particularlylimited, examples thereof include magnesium acetate, potassium acetate,magnesium propionate, potassium propionate, magnesium 2-ethylbutyrate,potassium 2-ethylbutanoate, magnesium 2-ethylhexanoate, potassium2-ethylhexanoate, and the like.

The total of the contents of Mg and K in a layer containing the Metalsalt M (a first layer, a second layer, or a third layer) is preferably 5ppm or more, more preferably 10 ppm or more, further preferably 20 ppmor more, and preferably 300 ppm or less, more preferably 250 ppm orless, and further preferably 200 ppm or less. When the total of thecontents of Mg and K is the above lower limit or more and the aboveupper limit or less, the adhesivity between the interlayer film and alamination glass member or the adhesivity between respective layers inthe interlayer film can be further well controlled.

(Ultraviolet Ray Screening Agent)

It is preferred that the interlayer film include an ultraviolet rayscreening agent. It is preferred that the first layer contain anultraviolet ray screening agent. It is preferred that the second layercontain an ultraviolet ray screening agent. It is preferred that thethird layer contain an ultraviolet ray screening agent. By the use of anultraviolet ray screening agent, even when the interlayer film and thelaminated glass are used for a long period of time, the visible lighttransmittance becomes further difficult to be lowered. One kind of theultraviolet ray screening agent may be used alone, and two or more kindsthereof may be used in combination.

Examples of the ultraviolet ray screening agent include an ultravioletray absorber. It is preferred that the ultraviolet ray screening agentbe an ultraviolet ray absorber.

Examples of the ultraviolet ray screening agent include an ultravioletray screening agent containing a metal atom, an ultraviolet rayscreening agent containing a metal oxide, an ultraviolet ray screeningagent having a benzotriazole structure, an ultraviolet ray screeningagent having a benzophenone structure, an ultraviolet ray screeningagent having a triazine structure, an ultraviolet ray screening agenthaving a malonic acid ester structure, an ultraviolet ray screeningagent having an oxanilide structure, an ultraviolet ray screening agenthaving a benzoate structure, and the like.

Examples of the ultraviolet ray screening agent containing a metal atominclude platinum particles, particles in which the surface of platinumparticles is coated with silica, palladium particles, particles in whichthe surface of palladium particles is coated with silica, and the like.It is preferred that the ultraviolet ray screening agent not be heatshielding particles.

The ultraviolet ray screening agent is preferably an ultraviolet rayscreening agent having a benzotriazole structure, an ultraviolet rayscreening agent having a benzophenone structure, an ultraviolet rayscreening agent having a triazine structure or an ultraviolet rayscreening agent having a benzoate structure, more preferably anultraviolet ray screening agent having a benzotriazole structure or anultraviolet ray screening agent having a benzophenone structure, andfurther preferably an ultraviolet ray screening agent having abenzotriazole structure.

Examples of the ultraviolet ray screening agent containing a metal oxideinclude zinc oxide, titanium oxide, cerium oxide, and the like.Furthermore, with regard to the ultraviolet ray screening agentcontaining a metal oxide, the surface thereof may be coated with anymaterial. Examples of the coating material for the surface of theultraviolet ray screening agent containing a metal oxide include aninsulating metal oxide, a hydrolyzable organosilicon compound, asilicone compound, and the like.

Examples of the ultraviolet ray screening agent having a benzotriazolestructure include ultraviolet ray screening agents having abenzotriazole structure such as2-(2′-hydroxy-5′-methylphenyl)benzotriazole (“Tinuvin P” available fromBASF Japan Ltd.), 2-(2′-hydroxy-3′,5′-di-t-butylphenyl)benzotriazole(“Tinuvin 320” available from BASF Japan Ltd.),2-(2′-hydroxy-3′-t-butyl-5-methylphenyl)-5-chlorobenzotriazole (“Tinuvin326” available from BASF Japan Ltd.) and2-(2′-hydroxy-3′,5′-di-amylphenyl)benzotriazole (“Tinuvin 328” availablefrom BASF Japan Ltd.). It is preferred that the ultraviolet rayscreening agent be an ultraviolet ray screening agent having abenzotriazole structure containing a halogen atom, and it is morepreferred that the ultraviolet ray screening agent be an ultraviolet rayscreening agent having a benzotriazole structure containing a chlorineatom, because those are excellent in ultraviolet ray absorbingperformance.

Examples of the ultraviolet ray screening agent having a benzophenonestructure include octabenzone (“Chimassorb 81” available from BASF JapanLtd.), and the like.

Examples of the ultraviolet ray screening agent having a triazinestructure include “LA-F70” available from ADEKA CORPORATION,2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[(hexyl)oxy]-phenol (“Tinuvin1577FF” available from BASF Japan Ltd.), and the like.

Examples of the ultraviolet ray screening agent having a malonic acidester structure include dimethyl(p-methoxybenzylidene)malonate,tetraethyl-2,2-(1,4-phenylenedimethylidene)bismalonate,2-(p-methoxybenzylidene)-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)malonate,and the like.

Examples of a commercial product of the ultraviolet ray screening agenthaving a malonic acid ester structure include Hostavin B-CAP, HostavinPR-25 and Hostavin PR-31 (any of these is available from Clariant JapanK.K.).

Examples of the ultraviolet ray screening agent having an oxanilidestructure include a kind of oxalic acid diamide having a substitutedaryl group and the like on the nitrogen atom such asN-(2-ethylphenyl)-N′-(2-ethoxy-5-t-butylphenyl)oxalic acid diamide,N-(2-ethylphenyl)-N′-(2-ethoxy-phenyl)oxalic acid diamide and2-ethyl-2′-ethoxy-oxanilide (“Sanduvor VSU” available from ClariantJapan K.K.).

Examples of the ultraviolet ray screening agent having a benzoatestructure include2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate (“Tinuvin120” available from BASF Japan Ltd.), and the like.

From the viewpoint of further suppressing the lowering in visible lighttransmittance after the lapse of a certain period of time, in 100% byweight of a layer containing the ultraviolet ray screening agent (afirst layer, a second layer or a third layer), the content of theultraviolet ray screening agent is preferably 0.1% by weight or more,more preferably 0.2% by weight or more, further preferably 0.3% byweight or more, especially preferably 0.5% by weight or more, andpreferably 2.5% by weight or less, more preferably 2% by weight or less,further preferably 1% by weight or less and especially preferably 0.8%by weight or less. In particular, by setting the content of theultraviolet ray screening agent to be 0.2% by weight or more in 100% byweight of a layer containing the ultraviolet ray screening agent, withregard to the interlayer film and laminated glass, the lowering invisible light transmittance thereof after the lapse of a certain periodof time can be significantly suppressed.

(Oxidation Inhibitor)

It is preferred that the interlayer film include an oxidation inhibitor.It is preferred that the first layer contain an oxidation inhibitor. Itis preferred that the second layer contain an oxidation inhibitor. It ispreferred that the third layer contain an oxidation inhibitor. One kindof the oxidation inhibitor may be used alone, and two or more kindsthereof may be used in combination.

Examples of the oxidation inhibitor include a phenol-based oxidationinhibitor, a sulfur-based oxidation inhibitor, a phosphorus-basedoxidation inhibitor, and the like. The phenol-based oxidation inhibitoris an oxidation inhibitor having a phenol skeleton. The sulfur-basedoxidation inhibitor is an oxidation inhibitor containing a sulfur atom.The phosphorus-based oxidation inhibitor is an oxidation inhibitorcontaining a phosphorus atom.

It is preferred that the oxidation inhibitor be a phenol-based oxidationinhibitor or a phosphorus-based oxidation inhibitor.

Examples of the phenol-based oxidation inhibitor include2,6-di-t-butyl-p-cresol (BHT), butyl hydroxyanisole (BHA),2,6-di-t-butyl-4-ethylphenol, stearylβ-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,2,2′-methylenebis-(4-methyl-6-butylphenol),2,2′-methylenebis-(4-ethyl-6-t-butylphenol),4,4′-butylidene-bis-(3-methyl-6-t-butylphenol),1,1,3-tris-(2-methyl-hydroxy-5-t-butylphenyl)butane,tetrakis[methylene-3-(3′,5′-butyl-4-hydroxyphenyl)propionate]methane,1,3,3-tris-(2-methyl-4-hydroxy-5-t-butylphenol)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,bis(3,3′-t-butylphenol)butyric acid glycol ester,bis(3-t-butyl-4-hydroxy-5-methylbenzenepropanoicacid)ethylenebis(oxyethylene), and the like. One kind or two or morekinds among these oxidation inhibitors are suitably used.

Examples of the phosphorus-based oxidation inhibitor include tridecylphosphite, tris(tridecyl) phosphite, triphenyl phosphite, trinonylphenylphosphite, bis(tridecyl)pentaerithritol diphosphite,bis(decyl)pentaerithritol diphosphite, tris(2,4-di-t-butylphenyl)phosphite, bis(2,4-di-t-butyl-6-methylphenyl)ethyl ester phosphorousacid, tris(2,4-di-t-butylphenyl) phosphite,2,2′-methylenebis(4,6-di-t-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, and the like. One kind or two or more kindsamong these oxidation inhibitors are suitably used.

Examples of a commercial product of the oxidation inhibitor include“IRGANOX 245” available from BASF Japan Ltd., “IRGAFOS 168” availablefrom BASF Japan Ltd., “IRGAFOS 38” available from BASF Japan Ltd.,“Sumilizer BHT” available from Sumitomo Chemical Co., Ltd., “IRGANOX1010” available from BASF Japan Ltd., and the like.

With regard to the interlayer film and laminated glass, in order tomaintain high visible light transmittance thereof over a long period oftime, it is preferred that the content of the oxidation inhibitor be0.1% by weight or more in 100% by weight of the interlayer film or in100% by weight of the layer containing the oxidation inhibitor (a firstlayer, a second layer or a third layer). Moreover, since an effectcommensurate with the addition of an oxidation inhibitor is notattained, it is preferred that the content of the oxidation inhibitor be2% by weight or less in 100% by weight of the interlayer film or in 100%by weight of the layer containing the oxidation inhibitor.

(Other Ingredients)

Each of the first layer, the second layer and the third layer maycontain additives such as a coupling agent containing silicon, aluminumor titanium, a dispersing agent, a surfactant, a flame retardant, anantistatic agent, a pigment, a dye, an adhesive force regulating agent,a moisture-resistance improving agent, a fluorescent brightening agentand an infrared ray absorber, as necessary. One kind of these additivesmay be used alone, and two or more kinds thereof may be used incombination.

(Other Details of Interlayer Film for Laminated Glass)

From the viewpoint of enhancing the flexural rigidity of laminatedglass, the equivalent stiffness at 25° C. of the interlayer film is 2.4MPa or more. From the viewpoint of further enhancing the flexuralrigidity of laminated glass, the equivalent stiffness at 25° C. of theinterlayer film is preferably 3 MPa or more, more preferably 4 MPa ormore, further preferably 5 MPa or more, and especially preferably 9 MPaor more. The equivalent stiffness at 25° C. of the interlayer film ispreferably 30 MPa or less and more preferably 20 MPa or less.

In this connection, in order to enhance the equivalent stiffness, it ispreferred that the first layer contain silica particles. Moreover, inorder to enhance the equivalent stiffness, the degree of crosslinking ofa polyvinyl acetal resin in the first layer may be moderately enhanced.Furthermore, in order to enhance the equivalent stiffness, it ispreferred that the thickness of each layer be appropriately selected.

From the viewpoint of further enhancing the sound insulating propertiesof laminated glass, the glass transition temperature of the first layeris preferably 15° C. or less, more preferably 10° C. or less, furtherpreferably 5° C. or less, and especially preferably 0° C. or less. Theglass transition temperature of the first layer is preferably −20° C. ormore.

From the viewpoint of further enhancing the flexural rigidity oflaminated glass, it is preferred that the glass transition temperatureof the first layer be lower than the glass transition temperature ofeach of the second layer and the third layer. By making the first layer,which has a glass transition temperature lower than that of each of thesecond layer and the third layer, contain silica particles and providingan interlayer film with the second layer and the third layer which havea glass transition temperature higher than that of the first layer, theflexural rigidity of laminated glass is significantly improved. From theviewpoint of still further enhancing the flexural rigidity of laminatedglass, the absolute value of a difference between the glass transitiontemperature of the first layer and the glass transition temperature ofeach of the second layer and the third layer is preferably 10° C. ormore, more preferably 20° C. or more, further preferably 30° C. or more,and especially preferably 35° C. or more. The absolute value of adifference between the glass transition temperature of the first layerand the glass transition temperature of each of the second layer and thethird layer is preferably 70° C. or less.

Examples of a method of measuring the glass transition temperatureinclude a method of measuring an interlayer film obtained for theviscoelasticity with the use of a viscoelasticity measuring apparatus“DVA-200” available from IT KEISOKU SEIGYO K.K. immediately after beingstored for 12 hours under an environment of a room temperature of 23±2°C. and a humidity of 25±5%. It is preferred that the interlayer film becut into a size of 8 mm in longitudinal width by 5 mm in lateral widthand be measured, using the shear mode, for the glass transitiontemperature under the condition in which the temperature is increasedfrom −30° C. to 100° C. at a temperature increasing rate of 5° C./minuteand under the condition of a frequency of 1 Hz and a strain of 0.08%.

From the viewpoint of enhancing the flexural rigidity of laminatedglass, the Young's modulus at 25° C. of the first layer is preferably0.4 MPa or more, more preferably 0.6 MPa or more, further preferably 0.8MPa or more, and preferably 6 MPa or less, more preferably 5 MPa orless, and further preferably 4 MPa or less.

From the viewpoint of enhancing the flexural rigidity of laminatedglass, the Young's modulus at 25° C. of each of the second layer and thethird layer is preferably 3 MPa or more, more preferably 10 MPa or more,further preferably 100 MPa or more, and preferably 700 MPa or less, morepreferably 500 MPa or less, and further preferably 400 MPa or less.

In this connection, in order to adjust the Young's modulus within amoderate range, it is preferred that the first layer contain silicaparticles. Moreover, in order to adjust the Young's modulus within amoderate range, the degree of crosslinking of a polyvinyl acetal resinin the first layer may be moderately enhanced.

The thickness of the interlayer film is not particularly limited. Fromthe viewpoint of the practical aspect and the viewpoint of sufficientlyenhancing the penetration resistance and the flexural rigidity oflaminated glass, the thickness of the interlayer film is preferably 0.1mm or more, more preferably 0.25 mm or more, and preferably 3 mm orless, more preferably 2 mm or less, and further preferably 1.5 mm orless. When the thickness of the interlayer film is the above lower limitor more, the penetration resistance and the flexural rigidity oflaminated glass are enhanced. When the thickness of the interlayer filmis the above upper limit or less, the transparency of the interlayerfilm is further improved.

The thickness of the interlayer film is defined as T. The thickness ofthe first layer is preferably 0.0625T or more, more preferably 0.1T ormore, and preferably 0.4T or less, more preferably 0.375T or less,further preferably 0.25T or less, and still further preferably 0.15T orless. When the thickness of the first layer is 0.4T or less, theflexural rigidity is further improved.

The thickness of each of the second layer and the third layer ispreferably 0.3T or more, more preferably 0.3125T or more, furtherpreferably 0.375T or more, and preferably 0.9375T or less, and morepreferably 0.9T or less. The thickness of each of the second layer andthe third layer may be 0.46875T or less and may be 0.45T or less.Moreover, when the thickness of each of the second layer and the thirdlayer is the above lower limit or more and the above upper limit orless, the rigidity and the sound insulating properties of laminatedglass are further enhanced.

The total thickness of the second layer and the third layer ispreferably 0.625T or more, more preferably 0.75T or more, furtherpreferably 0.85T or more, and preferably 0.9375T or less, and morepreferably 0.9T or less. Moreover, when the total thickness of thesecond layer and the third layer is the above lower limit or more andthe above upper limit or less, the rigidity and the sound insulatingproperties of laminated glass are further enhanced.

The production method of the interlayer film according to the presentinvention is not particularly limited. Examples of the production methodof the interlayer film according to the present invention include amethod of separately forming respective resin compositions used forconstituting respective layers into respective layers, and then, forexample, layering the respective obtained layers, a method ofcoextruding respective resin compositions used for constitutingrespective layers with an extruder and layering the respective layers,and the like. A production method of extrusion-molding is preferredbecause the method is suitable for continuous production.

Since the production efficiency of the interlayer film is excellent, itis preferred that respective polyvinyl acetal resins contained in thesecond layer and the third layer be the same as each other, it is morepreferred that respective polyvinyl acetal resins contained in thesecond layer and the third layer be the same as each other andrespective plasticizers contained therein be the same as each other, andit is further preferred that the second layer and the third layer beformed from the same resin composition as each other.

It is preferred that at least one surface among surfaces of both sidesof the interlayer film have a recess/protrusion shape. It is morepreferred that surfaces of both sides of the interlayer film have arecess/protrusion shape. The method for forming the recess/protrusionshape is not particularly limited, and examples thereof include a lipemboss method, an embossing roll method, a calendar roll method, aprofile extrusion method, and the like. Since it is possible toquantitatively form many embosses with a recess/protrusion shapeconstituting a constant uneven pattern, the embossing roll method ispreferred.

(Laminated Glass)

FIG. 2 is a sectional view schematically showing an example of laminatedglass prepared with the interlayer film for laminated glass shown inFIG. 1.

The laminated glass 31 shown in FIG. 2 is provided with a firstlamination glass member 21, a second lamination glass member 22, and aninterlayer film 11. The interlayer film 11 is arranged between the firstlamination glass member 21 and the second lamination glass member 22 tobe sandwiched therebetween.

The first lamination glass member 21 is layered on a first surface 11 aof the interlayer film 11. The second lamination glass member 22 islayered on a second surface 11 b opposite to the first surface 11 a ofthe interlayer film 11. The first lamination glass member 21 is layeredon an outer surface 2 a of a second layer 2. The second lamination glassmember 22 is layered on an outer surface 3 a of a third layer 3.

As described above, the laminated glass according to the presentinvention is provided with a first lamination glass member, a secondlamination glass member, and an interlayer film and the interlayer filmis the interlayer film for laminated glass according to the presentinvention. In the laminated glass according to the present invention,the above-mentioned interlayer film is arranged between the firstlamination glass member and the second lamination glass member.

Examples of the lamination glass member include a glass plate, a PET(polyethylene terephthalate) film, and the like. As the laminated glass,laminated glass in which an interlayer film is sandwiched between aglass plate and a PET film or the like, as well as laminated glass inwhich an interlayer film is sandwiched between two glass plates, isincluded. The laminated glass is a laminate provided with a glass plate,and it is preferred that at least one glass plate be used.

Examples of the glass plate include a sheet of inorganic glass and asheet of organic glass. Examples of the inorganic glass include floatplate glass, heat ray-absorbing plate glass, heat ray-reflecting plateglass, polished plate glass, figured glass, wired plate glass, and thelike. The organic glass is synthetic resin glass substituted forinorganic glass. Examples of the organic glass include a polycarbonateplate, a poly(meth)acrylic resin plate, and the like. Examples of thepoly(meth)acrylic resin plate include a polymethyl (meth)acrylate plate,and the like.

The thickness of the lamination glass member is preferably 1 mm or more,and preferably 5 mm or less, and more preferably 3 mm or less. Moreover,when the lamination glass member is a glass plate, the thickness of theglass plate is preferably 0.5 mm or more, more preferably 0.7 mm ormore, and preferably 5 mm or less, and more preferably 3 mm or less.When the lamination glass member is a PET film, the thickness of the PETfilm is preferably 0.03 mm or more and preferably 0.5 mm or less.

By the use of the interlayer film according to the present invention,the flexural rigidity of laminated glass can be maintained high evenwhen the thickness of the laminated glass is thinned. From theviewpoints of attaining reduced weight of laminated glass and decreasingthe amount of the material for laminated glass to reduce theenvironmental load, and improving fuel consumption of an automobile byreduction in weight of laminated glass to reduce the environmental load,the thickness of the glass plate is preferably 2 mm or less, morepreferably less than 2 mm, even more preferably 1.8 mm or less, evenmore preferably 1.5 mm or less, further preferably 1 mm or less, stillfurther preferably 0.8 mm or less, and especially preferably 0.7 mm orless.

The method for producing the laminated glass is not particularlylimited. For example, the interlayer film is sandwiched between thefirst lamination glass member and the second lamination glass member,and then, passed through pressure rolls or subjected to decompressionsuction in a rubber bag, so that the air remaining between the first andthe second lamination glass members and the interlayer film is removed.Afterward, the members are preliminarily bonded together at about 70 to110° C. to obtain a laminate. Next, by putting the laminate into anautoclave or by pressing the laminate, the members are press-bondedtogether at about 120 to 150° C. and under a pressure of 1 to 1.5 MPa.In this way, laminated glass can be obtained. At the time of producingthe laminated glass, a first layer, a second layer, and a third layermay be layered.

Each of the interlayer film and the laminated glass can be used forautomobiles, railway vehicles, aircraft, ships, buildings and the like.Each of the interlayer film and the laminated glass can also be used forapplications other than these applications. It is preferred that theinterlayer film and the laminated glass be an interlayer film andlaminated glass for vehicles or for building respectively, and it ismore preferred that the interlayer film and the laminated glass be aninterlayer film and laminated glass for vehicles respectively. Each ofthe interlayer film and the laminated glass can be used for awindshield, side glass, rear glass or roof glass of an automobile, andthe like. The interlayer film and the laminated glass are suitably usedfor automobiles. The interlayer film is suitably used for obtaininglaminated glass of an automobile.

From the viewpoint of obtaining laminated glass further excellent intransparency, the visible light transmittance of laminated glass ispreferably 65% or more and more preferably 70% or more. The visiblelight transmittance of laminated glass can be measured in accordancewith JIS R3211 (1998). It is preferred that the visible lighttransmittance of laminated glass obtained by sandwiching the interlayerfilm for laminated glass according to the present invention between twosheets of green glass (heat ray-absorbing plate glass) with a thicknessof 2 mm in accordance with JIS R3208 be 70% or more. The visible lighttransmittance is more preferably 75% or more.

Hereinafter, the present invention will be described in more detail withreference to examples. The present invention is not limited only tothese examples.

The following materials were prepared.

(Polyvinyl Acetal Resin)

Polyvinyl acetal resins shown in the following Table 1 were used. In allpolyvinyl acetal resins used, n-butyraldehyde which has 4 carbon atomsis used for the acetalization. With regard to the polyvinyl acetalresin, the acetalization degree (the butyralization degree), theacetylation degree, and the content of the hydroxyl group were measuredby a method in accordance with JIS K6728 “Testing methods for polyvinylbutyral”. In this connection, even in the cases of being measuredaccording to ASTM D1396-92, numerical values similar to those obtainedby a method in accordance with JIS K6728 “Testing methods for polyvinylbutyral” were exhibited.

(Plasticizer)

Triethylene glycol di-2-ethylhexanoate (3GO)

(Ultraviolet Ray Screening Agent)

Tinuvin 326(2-(2′-hydroxy-3′-t-butyl-5-methylphenyl)-5-chlorobenzotriazole,“Tinuvin 326” available from BASF Japan Ltd.)

(Oxidation Inhibitor)

BHT (2,6-di-t-butyl-p-cresol)

EXAMPLE 1

Preparation of Composition for Forming First Layer:

One hundred parts by weight of a polyvinyl acetal resin of a kind shownin the following Table 1, 60 parts by weight of a plasticizer (3GO), 0.2parts by weight of an ultraviolet ray screening agent (Tinuvin 326), and0.2 parts by weight of an oxidation inhibitor (BHT) were mixed to obtaina composition for forming a first layer.

Preparation of Composition for Forming Second and Third Layers:

One hundred parts by weight of a polyvinyl acetal resin of a kind shownin the following Table 1, 34 parts by weight of a plasticizer (3GO), 0.2parts by weight of an ultraviolet ray screening agent (Tinuvin 326), and0.2 parts by weight of an oxidation inhibitor (BHT) were mixed to obtaina composition for forming a second layer and a third layer.

Preparation of Interlayer Film:

The composition for forming a first layer and the composition forforming a second layer and a third layer were coextruded with acoextruder to prepare an interlayer film (780 μm in thickness) having alayered structure with a stack of a second layer (340 μm in thickness)/afirst layer (100 μm in thickness)/a third layer (340 μm in thickness).

Preparation of Laminated Glass A (for Flexural Rigidity Measurement):

Two washed and dried glass plates (clear float glass, 25 cm inlongitudinal length×10 cm in transversal length×0.7 mm in thickness)were prepared. The obtained interlayer film was sandwiched between thetwo glass plates to obtain a laminate. The obtained laminate was putinto a rubber bag and the inside thereof was degassed for 20 minutes ata degree of vacuum of 2660 Pa (20 torr). Afterward, while keeping thelaminate degassed, furthermore, the laminate was held in place for 30minutes at 90° C. and pressed under vacuum in an autoclave. The laminatethus preliminarily press-bonded was subjected to press-bonding for 20minutes under conditions of 135° C. and a pressure of 1.2 MPa (12kg/cm²) in an autoclave to obtain a sheet of Laminated glass A.

Preparation of Laminated Glass B (for Sound Insulating PropertiesMeasurement):

The obtained interlayer film was cut into a size of 30 cm inlongitudinal length×2.5 cm in transversal length. Next, between twosheets of green glass (30 cm in longitudinal length×2.5 cm intransversal length×2 mm in thickness) in accordance with JIS R3208, theinterlayer film was sandwiched to obtain a laminate. The laminate wasput into a rubber bag and the inside thereof was degassed for 20 minutesat a degree of vacuum of 2.6 kPa, after which the laminate wastransferred into an oven while keeping the laminate degassed, andfurthermore, held in place for 30 minutes at 90° C. and pressed undervacuum to subject the laminate to preliminary press-bonding. Thepreliminarily press-bonded laminate was subjected to press-bonding for20 minutes under conditions of 135° C. and a pressure of 1.2 MPa in anautoclave to obtain a sheet of Laminated glass B.

EXAMPLES 2 TO 12 AND COMPARATIVE EXAMPLES 1 TO 10

An interlayer film and a sheet of laminated glass were obtained in thesame manner as that in Example 1 except that the kind and blendingamount of each of the polyvinyl acetal resin and the plasticizer whichare used for a composition for forming a first layer and a compositionfor forming a second layer and a third layer were set to those listed inthe following Tables 1 and 2 and the thicknesses of the first layer, thesecond layer, and the third layer were set to those listed in thefollowing Tables 1 and 2. Moreover, in Examples 2 to 12 and ComparativeExamples 1 to 10, each of the ultraviolet ray screening agent and theoxidation inhibitor of the same kind as that in Example 1 was blended inthe same blending amount (0.2 parts by weight relative to 100 parts byweight of the polyvinyl acetal resin) as that in Example 1.

(Evaluation)

(1) Determination of content Y of plasticizer in interlayer film forlaminated glass relative to 100 parts by weight of polyvinyl acetalresin in interlayer film for laminated glass

An interlayer film for laminated glass was cut into a size of 0.5 cm inlongitudinal length by 5 cm in transversal length, and in the case ofthe three-layer structure with a stack of the second layer, the firstlayer, and the third layer, the interlayer film for laminated glass wasallowed to stand for 12 hours under an environment of 23±2° C. and ahumidity of 25±5%, after which the second layer was peeled off from thefirst layer, and then, the third layer was peeled off from the firstlayer. The weight of the peeled first layer was measured with the use ofan electronic balance for analysis (GH-200 available from A&D Company,Limited) and the weight of the peeled first layer was defined as X1(mg). With the use of a gas chromatograph (GC-2014 available fromSHIMADZU CORPORATION), the peeled first layer was measured for thepercentage content (R1) occupied by the polyvinyl acetal resin in thetotal of the polyvinyl acetal resin and the plasticizer contained in thefirst layer and the percentage content (P1) occupied by the plasticizerin the total of the polyvinyl acetal resin and the plasticizer containedin the first layer. In this connection, R1 mentioned above wascalculated by dividing the content of the polyvinyl acetal resin in thefirst layer by the total content of the polyvinyl acetal resin and theplasticizer in the first layer and P1 mentioned above was calculated bydividing the content of the plasticizer in the first layer by the totalcontent of the polyvinyl acetal resin and the plasticizer in the firstlayer. Similarly, the weight X2 (mg) of the second layer, the percentagecontent (R2) occupied by the polyvinyl acetal resin in the total of thepolyvinyl acetal resin and the plasticizer contained in the secondlayer, and the percentage content (P2) occupied by the plasticizer inthe total of the polyvinyl acetal resin and the plasticizer contained inthe second layer were measured. Similarly, the weight X3 (mg) of thethird layer, the percentage content (R3) occupied by the polyvinylacetal resin in the total of the polyvinyl acetal resin and theplasticizer contained in the third layer, and the percentage content(P3) occupied by the plasticizer in the total of the polyvinyl acetalresin and the plasticizer contained in the third layer were measured.Furthermore, the content of the polyvinyl acetal resin in the firstlayer was calculated as X1 (mg)×R1, the content of the polyvinyl acetalresin in the second layer was calculated as X2 (mg)×R2, the content ofthe polyvinyl acetal resin in the third layer was calculated as X3(mg)×R3, and the content of the polyvinyl acetal resin in the interlayerfilm for laminated glass was defined as X1 (mg)×R1+X2 (mg)×R2+X3(mg)×R3. Similarly, the content of the plasticizer in the first layerwas calculated as X1 (mg)×P1, the content of the plasticizer in thesecond layer was calculated as X2 (mg)×P2, the content of theplasticizer in the third layer was calculated as X3 (mg)×P3, and thecontent of the plasticizer in the interlayer film for laminated glasswas defined as X1 (mg)×P1+X2 (mg)×P2+X3 (mg)×P3. From the results, thecontent Y of the plasticizer in the interlayer film for laminated glassrelative to 100 parts by weight of the polyvinyl acetal resin in theinterlayer film for laminated glass was calculated as [{X1 (mg)×P1+X2(mg)×P2+X3 (mg)×P3}/{X1 (mg)×R1+X2 (mg)×R2+X3 (mg)×R3}]. In thisconnection, the percentage content (R1) occupied by the polyvinyl acetalresin in the first layer and the percentage content (P1) occupied by theplasticizer therein were determined by the GC measurement according tothe following procedure. A 0.05-g portion of a film obtained by beingpeeled off was weighed accurately and dissolved in 4 ml of a solvent inwhich methanol and chloroform were mixed at a weight ratio of 1:1. With1.9 ml of a 1:1 mixed solvent of methanol/chloroform, 0.1 ml of themixed-solvent solution was diluted. The solution after dilution wasfiltered through a syringe filter of 0.2 μm to prepare a solution for GCmeasurement. GC measurement conditions were set as follows. The inlettemperature was set to 280° C., HP-5 (0.32 mmΩ×30 m×0.25 μm, availablefrom Agilent Technologies Japan, Ltd.) was used as a column, and thecolumn temperature was set so as to be maintained for 1 minute at 80°C., then, elevated at 20° C./minute, and maintained for 30 seconds at320° C. Helium was adopted as a carrier gas, the flow rate was set to2.0 ml/minute, and the split ratio was set to 1:10. The injection volumeof a sample solution was set to 2 μl, a hydrogen flame ionizationdetector (FID) was used as a detector, and the temperature of thedetector was set to 320° C. With the use of a calibration curve of theplasticizer prepared in advance on the same day, the percentage content(P1) of the plasticizer in the sample solution was calculated. Moreover,the percentage content (R1) of the polyvinyl acetal resin was calculatedfrom the formula of 1−P1. Although additives other than the polyvinylacetal resin and the plasticizer contained in the interlayer film arealso included in the percentage content R1, this may be ignored becausethese additives are contained in trace amounts. Similarly, the secondlayer and the third layer were also subjected to the GC measurement.

(2) Flexural Rigidity

The sheet of Laminated glass A obtained was prepared. The flexuralrigidity was evaluated by the testing method schematically shown in FIG.3. As a measuring apparatus, the universal testing machine 5966, whichis available from INSTRON Japan Co., Ltd. and equipped with the static3-point flexural test jig 2810, was used. Under measurement conditionsof the measurement temperature of 20±3° C., the distance D1 of 18 cm,and the distance D2 of 25 cm, a sheet of laminated glass was deformed inthe F direction at a displacement rate of 1 mm/minute and the stress atthe time when the deformation amount becomes 1.5 mm was measured tocalculate the flexural rigidity. In this connection, with regard to theflexural rigidity, a sheet of laminated glass after one day had elapsedfrom the production was measured for Flexural rigidity δ (1D) and asheet of laminated glass stored for 3 months under an environment of 20°C. after the production was measured for Flexural rigidity δ (3M),respectively.

(3) Sound Insulating Properties

A sheet of Laminated glass B was excited by means of a vibrationgenerator for a damping test (“Vibration exciter G21-005D” availablefrom SHINKEN CO., LTD.) to obtain vibration characteristics, thevibration characteristics were amplified by a mechanical impedancemeasuring apparatus (“XG-81” available from RION Co., Ltd.), and thevibration spectrum was analyzed by an FFT spectrum analyzer (“FFTanalyzer HP3582A” available from Yokogawa-Hewlett-Packard, Ltd.).

From the ratio of the loss factor thus obtained to the resonancefrequency of laminated glass, a graph showing the relationship betweenthe sound frequency (Hz) and the sound transmission loss (dB) at 20° C.was prepared to determine the minimum sound transmission loss (TL value)at a sound frequency of about 2,000 Hz. The higher this TL value is, thehigher in sound insulating properties of laminated glass is. The soundinsulating properties were judged according to the following criteria.

[Criteria for Judgment in Sound Insulating Properties]

◯: The TL value is 35 dB or more.

x: The TL value is less than 35 dB.

The details and the results are shown in the following Tables 1 and 2.In this connection, in the following Tables 1 and 2, the description ofingredients to be blended other than the polyvinyl acetal resin and theplasticizer was omitted.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Example 8 Example 9 Example 10 Example 11 Example 12Composition Thickness μm 100 100 100 100 100 100 100 100 100 100 100 100for forming Polyvinyl Average 3000 3000 3000 3000 3000 3000 3000 30003000 3000 3000 3000 first layer acetal polymerization resin degree ofPVA Content of % by mole 23.8 23.8 23.8 23.8 23.1 23.1 23.1 23.1 23.123.1 23.1 23.1 hydroxyl group Acetylation % by mole 12.1 12.1 12.1 12.112.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 degree Acetalization % by mole64.1 64.1 64.1 64.1 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 degreeContent Parts by weight 100 100 100 100 100 100 100 100 100 100 100 100Plasticizer Kind 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO ContentParts by weight 60 60 60 60 60 60 60 60 60 60 60 60 CompositionRespective thicknesses μm 340 340 340 340 340 340 340 340 340 340 340340 for forming Polyvinyl Average 1700 1700 1700 1700 1700 1700 17001700 1700 1700 1700 1700 second and acetal polymerization third layersresin degree of PVA Content of % by mole 34.5 34.5 34.5 34.5 33.2 33.233.2 33.2 32.5 32.5 32.5 32.5 hydroxyl group Acetylation % by mole 0.80.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 degree Acetalization % bymole 64.7 64.7 64.7 64.7 66 66 66 66 66.7 66.7 66.7 66.7 degree ContentParts by weight 100 100 100 100 100 100 100 100 100 100 100 100Plasticizer Kind 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO ContentParts by weight 34 32 30 28 36 34 32 30 37 35 33 31 Absolute value ofdifference between % by mole 10.7 10.7 10.7 10.7 10.1 10.1 10.1 10.1 9.49.4 9.4 9.4 content of hydroxyl group of polyvinyl acetal resin in firstlayer and content of hydroxyl group of polyvinyl acetal resin in each ofsecond and third layers Content Y Parts by weight 36.9 35.0 33.2 31.438.7 36.9 35.0 33.2 39.6 37.8 35.9 34.1 Evaluation Flexural rigidity δ(1 D) N/mm 11.90 12.56 13.19 13.80 11.32 12.03 12.71 13.36 10.87 11.6112.32 13.00 δ (3 M) N/mm 9.13 9.79 10.42 11.03 8.97 9.65 10.30 10.928.85 9.54 10.20 10.84 Sound insulating properties: TL method ◯ ◯ ◯ ◯ ◯ ◯◯ ◯ ◯ ◯ ◯ ◯

TABLE 2 Comparative Comparative Comparative Comparative ComparativeComparative Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8Example 9 Example 10 Composition Thickness μm 100 100 100 100 100 100127 127 127 127 for forming Polyvinyl Average 3000 3000 3000 3000 30003000 2300 2300 2300 2300 first layer acetal polymerization resin degreeof PVA Content of % by mole 23.8 23.1 23.1 23.8 23.1 23.1 18.4 18.4 18.418.4 hydroxyl group Acetylation % by mole 12.1 12.5 12.5 12.1 12.5 12.51.7 1.7 1.7 1.7 degree Acetalization % by mole 64.1 64.5 64.5 64.1 64.564.5 79.9 79.9 79.9 79.9 degree Content Parts by weight 100 100 100 100100 100 100 100 100 100 Plasticizer Kind 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO3GO 3GO Content Parts by weight 60 60 60 60 60 60 75 75 75 75Composition Respective thicknesses μm 340 340 340 340 340 340 330 356330 330 for forming Polyvinyl Average 1700 1700 1700 1700 1700 1700 17001700 1700 1700 second and acetal polymerization third layers resindegree of PVA Content of % by mole 34.5 33.2 32.5 34.5 33.2 32.5 30.127.2 29.4 29.4 hydroxyl group Acetylation % by mole 0.8 0.8 0.8 0.8 0.80.8 1.7 1.7 1.7 1.7 degree Acetalization % by mole 64.7 66 66.7 64.7 6666.7 68.2 71.1 68.9 68.9 degree Content Parts by weight 100 100 100 100100 100 100 100 100 100 Plasticizer Kind 3GO 3GO 3GO 3GO 3GO 3GO 3GO 3GO3GO 3GO Content Parts by weight 36 38 39 38 40 41 35 38 35 34 Absolutevalue of difference between % by mole 10.7 10.1 9.4 10.7 10.1 9.4 11.78.8 11.0 11.0 content of hydroxyl group of polyvinyl acetal resin infirst layer and content of hydroxyl group of polyvinyl acetal resin ineach of second and third layers Content Y Parts by weight 38.7 40.5 41.440.5 42.3 43.2 40.2 42.6 40.2 39.3 Evaluation Flexural rigidity δ (1 D)N/mm 11.20 10.58 10.10 10.49 9.81 9.31 9.76 8.19 9.87 10.08 δ (3 M) N/mm8.44 8.26 8.13 7.70 7.52 7.40 8.03 7.54 8.15 8.24 Sound insulatingproperties: TL method ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯

EXPLANATION OF SYMBOLS

-   -   1: First layer    -   1 a: First surface    -   1 b: Second surface    -   2: Second layer    -   2 a: Outer surface    -   3: Third layer    -   3 a: Outer surface    -   11: Interlayer film    -   11A: Interlayer film (First layer)    -   11 a: First surface    -   11 b: Second surface    -   21: First lamination glass member    -   22: Second lamination glass member    -   31: Laminated glass

1. An interlayer film for laminated glass, having a three or more-layerstructure and containing a polyvinyl acetal resin and a plasticizer,comprising: a first layer containing a polyvinyl acetal resin and aplasticizer; a second layer being layered on a first surface of thefirst layer and containing a polyvinyl acetal resin and a plasticizer;and a third layer being layered on a second surface opposite to thefirst surface of the first layer and containing a polyvinyl acetal resinand a plasticizer, the content of the hydroxyl group of the polyvinylacetal resin in the first layer being lower than the content of thehydroxyl group of the polyvinyl acetal resin in the second layer, andwhen an absolute value of a difference between the content of thehydroxyl group of the polyvinyl acetal resin in the second layer and thecontent of the hydroxyl group of the polyvinyl acetal resin in the firstlayer is defined as XA, the absolute value XA being 9% by mole or moreand 11% by mole or less, the content of the hydroxyl group of thepolyvinyl acetal resin in the first layer being lower than the contentof the hydroxyl group of the polyvinyl acetal resin in the third layer,and when an absolute value of a difference between the content of thehydroxyl group of the polyvinyl acetal resin in the third layer and thecontent of the hydroxyl group of the polyvinyl acetal resin in the firstlayer is defined as XB, the absolute value XB being 9% by mole or moreand 1% by mole or less, and when a content of the plasticizer in theinterlayer film for laminated glass relative to 100 parts by weight ofthe polyvinyl acetal resin in the interlayer film for laminated glass isdefined as Y, XA, XB, and Y satisfying the equations of Y≤−1.68XA+56 andY≤−1.68XB+56.
 2. The interlayer film for laminated glass according toclaim 1, wherein the content of the plasticizer in the first layerrelative to 100 parts by weight of the polyvinyl acetal resin in thefirst layer is larger than the content of the plasticizer in the secondlayer relative to 100 parts by weight of the polyvinyl acetal resin inthe second layer.
 3. The interlayer film for laminated glass accordingto claim 1, wherein the content of the plasticizer in the first layerrelative to 100 parts by weight of the polyvinyl acetal resin in thefirst layer is larger than the content of the plasticizer in the thirdlayer relative to 100 parts by weight of the polyvinyl acetal resin inthe third layer.
 4. The interlayer film for laminated glass according toclaim 1, wherein the content of the hydroxyl group of the polyvinylacetal resin in the second layer is 32% by mole or more.
 5. Theinterlayer film for laminated glass according to claim 1, wherein thecontent of the hydroxyl group of the polyvinyl acetal resin in the thirdlayer is 32% by mole or more.
 6. The interlayer film for laminated glassaccording to claim 1, wherein the absolute value XA is more than 9.3% bymole.
 7. The interlayer film for laminated glass according to claim 1,wherein the absolute value XB is more than 9.3% by mole.
 8. Theinterlayer film for laminated glass according to claim 1, wherein thecontent of the plasticizer in the first layer relative to 100 parts byweight of the polyvinyl acetal resin in the first layer is 55 parts byweight or more and 100 parts by weight or less.
 9. The interlayer filmfor laminated glass according to claim 1, wherein each of the content ofthe plasticizer in the second layer relative to 100 parts by weight ofthe polyvinyl acetal resin in the second layer and the content of theplasticizer in the third layer relative to 100 parts by weight of thepolyvinyl acetal resin in the third layer is 50 parts by weight or less.10. The interlayer film for laminated glass according to claim 1,wherein the content Y of the plasticizer in the interlayer film forlaminated glass relative to 100 parts by weight of the polyvinyl acetalresin in the interlayer film for laminated glass is 25 parts by weightor more and 40 parts by weight or less.
 11. The interlayer film forlaminated glass according to claim 1, wherein the polyvinyl acetal resinin the first layer is a polyvinyl butyral resin, the polyvinyl acetalresin in the second layer is a polyvinyl butyral resin, and thepolyvinyl acetal resin in the third layer is a polyvinyl butyral resin.12. The interlayer film for laminated glass according to claim 1, beingused together with a first glass plate having a thickness of less than 2mm and being arranged between the first glass plate and a second glassplate to obtain laminated glass.
 13. Laminated glass, comprising: afirst lamination glass member; a second lamination glass member; and theinterlayer film for laminated glass according to claim 1, the interlayerfilm for laminated glass being arranged between the first laminationglass member and the second lamination glass member.
 14. The laminatedglass according to claim 13, wherein the first lamination glass memberis a first glass plate and the thickness of the first glass plate isless than 2 mm.